Absorbent cores having material free areas

ABSTRACT

An absorbent core ( 28 ), for use in an absorbent article, comprising a core wrap ( 16, 16 ′) enclosing an absorbent material ( 60 ) comprising superabsorbent polymer particles. The core wrap comprises a top side ( 16 ) and a bottom side ( 16 ′), and the absorbent core comprises one or more area(s) ( 26 ) substantially free of absorbent material through which the top side of the core wrap is attached to the bottom side of the core wrap, so that when the absorbent material swells the core wrap forms one or more channel(s) ( 26 ′) along the area(s) ( 26 ) substantially free of absorbent material. The superabsorbent polymer particles have a time to reach an uptake of 20 g/g (T20) of less than 240 s as measured according to the K(t) test method.

FIELD OF THE INVENTION

The invention provides absorbent cores for use in absorbent hygienearticles such as, but not limited to, baby diapers, training pants,feminine hygiene sanitary pads and adult incontinence products.

BACKGROUND OF THE INVENTION

Absorbent articles for personal hygiene of the type indicated above aredesigned to absorb and contain body exudates, in particular largequantity of urine. These absorbent articles comprise several layersproviding different functions, for example a topsheet, a backsheet andin-between an absorbent core, among other layers. The function of theabsorbent core is typically to absorb and retain the exudates for aprolonged amount of time, minimize re-wet to keep the wearer dry andavoid soiling of clothes or bed sheets.

The majority of currently marketed absorbent articles comprise asabsorbent material a blend of comminuted wood pulp with superabsorbentpolymers (SAP) in particulate form, also called absorbent gellingmaterials (AGM), see for example U.S. Pat. No. 5,151,092 (Buell).Absorbent articles having a core consisting essentially of SAP asabsorbent material (so called “airfelt-free” cores) have also beenproposed (see e.g. WO2008/155699 (Hundorf), WO95/11652 (Tanzer),WO2012/052172 (Van Malderen)). Absorbent cores with slits or grooveshave also been proposed, typically to increase the fluid acquisitionproperties of the core or to act as a folding guide.

WO2012/170778 (Rosati et al., see also WO2012/170779, WO2012/170781 andWO2012/170808) discloses absorbent structures that comprisesuperabsorbent polymers, optionally a cellulosic material, and at leasta pair of substantially longitudinally extending channels. The core wrapcan be adhesively bonded through the channels to form a channel bond.The channel bonds may be permanent, so that their integrity is at leastpartially maintained both in dry and wet state. As the absorbentstructure absorbs liquid and swells, the absorbent structure takes athree-dimensional shape with the channels becoming visible. The channelsare indicated to provide improved fit and/or better liquidacquisition/transportation, and/or improved performance throughout theuse of the absorbent structure. Any superabsorbent polymer particlesknown from the superabsorbent literature are indicated to be suitable.

The properties of superabsorbent polymers have been characterized invarious ways. The absorbent capacity (CRC) in grams of liquid per gramof superabsorbent particles has been used, as well as their absorptionspeed as measured by the Free Swell Rate (FSR) and their permeability asmeasured by the Urine Permeability Measurement (UPM) test.

International patent application WO2012/174,026A1 discloses the K(t)method which can be used to determine the time dependent effectivepermeability (K(t)) and the uptake kinetics (T20) of a gel layer formedfrom hydrogel-forming superabsorbent polymer particles under a confiningpressure. The application indicates that these SAP can be used to reduceleakage, especially at the first gush, i.e. when the article starts tobe wetted.

It has now been found that although the absorption properties ofconventional SAP may not be negatively impacted at first gush when usedin a core with channels, the liquid absorption of the SAP can besignificantly reduced in the following gushes after the fluid has beenalready absorbed in these cores comprising channels compared to coreswithout channels. Without wishing to be bound by theory, the inventorsbelieve that the three-dimensional channels which are formed as the SAPabsorbs a fluid can create a resistance to swelling for thesuperabsorbent polymers and reduce their swelling kinetics. As thechannels otherwise facilitate the distribution of the fluid along thecore, it was on contrary expected that any conventional SAP could beused in these cores. Accordingly the inventors have found that forabsorbent cores comprising such channels it can be advantageous to usethese SAP having a T20 of below 240 s to maintain sufficient speed ofabsorption beyond first gush.

SUMMARY OF THE INVENTION

The present invention is for absorbent cores as defined in the claimsand absorbent articles comprising these absorbent cores. The absorbentcores of the invention comprise in particular a core wrap enclosing anabsorbent material comprising superabsorbent polymer particles, whereinthe core wrap comprises a top side and a bottom side. The absorbent corecomprises one or more area(s) substantially free of absorbent materialthrough which the top side of the core wrap is attached to the bottomside of the core wrap, so that when the absorbent material swells thecore wrap forms a channel along each area substantially free ofabsorbent material. The superabsorbent polymer particles have a time toreach an uptake of 20 g/g (T20) of less than 240 s as measured accordingto the K(t) test method described herein.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a top view of an embodiment of an absorbent core according tothe invention with the topside layer of the core wrap partially removed;

FIG. 2 is a transversal cross-section of the embodiment of FIG. 1 at thecrotch point (C);

FIG. 3 is a longitudinal cross-section of the embodiment of FIG. 1;

FIG. 4 is a close-up view of a part of FIG. 3

FIG. 5 is a top view of an exemplary absorbent article in the form adiaper with an absorbent core of the invention.

FIG. 6 is a transversal cross-section of the article of FIG. 5;

FIG. 7 is a transversal cross-section of the article taken at the samepoint as FIG. 6 where channels have formed in the core as a result ofthe diaper being loaded with fluid.

FIG. 8 is a sketch of a vacuum table which was used to make theexemplary absorbent cores 1 and 3 described below.

FIG. 9 is a partial cross-sectional side view of a suitable permeabilitymeasurement system for conducting the Dynamic Effective Permeability andUptake Kinetics Measurement Test.

FIG. 10 is a cross-sectional side view of a piston/cylinder assembly foruse in conducting the Dynamic Effective Permeability and Uptake KineticsMeasurement Test

FIG. 11 is a top view of a piston head suitable for use in thepiston/cylinder assembly shown in FIG. 10.

DETAILED DESCRIPTION OF THE INVENTION Introduction

As used herein, the term “absorbent articles for personal hygiene”refers to disposable devices such as baby diapers, infant trainingpants, adult incontinence products or feminine hygiene sanitary pads,and the like which are placed against or in proximity to the body of thewearer to absorb and contain exudates discharged from the body. Theabsorbent articles of the invention will be further illustrated in thebelow description and in the Figures in the form of a taped diaper.Nothing in this description should be however considered limiting thescope of the claims unless explicitly indicated otherwise.

A “nonwoven web” as used herein means a manufactured sheet, web orbatting of directionally or randomly orientated fibers, bonded byfriction, and/or cohesion and/or adhesion, excluding paper and productswhich are woven, knitted, tufted, stitch-bonded incorporating bindingyarns or filaments, or felted by wet-milling, whether or notadditionally needled. The fibers may be of natural or man-made originand may be staple or continuous filaments or be formed in situ.Commercially available fibers have diameters ranging from less thanabout 0.001 mm to more than about 0.2 mm and they come in severaldifferent forms such as short fibers (known as staple, or chopped),continuous single fibers (filaments or monofilaments), untwisted bundlesof continuous filaments (tow), and twisted bundles of continuousfilaments (yarn). Nonwoven webs can be formed by many processes such asmeltblowing, spunbonding, solvent spinning, electrospinning, carding andairlaying. The basis weight of nonwoven webs is usually expressed ingrams per square meter (g/m² or gsm).

The term “joined” or “bonded” or “attached”, as used herein, encompassesconfigurations whereby an element is directly secured to another elementby affixing the element directly to the other element e.g. by gluing,and configurations whereby an element is indirectly secured to anotherelement by affixing the element to intermediate member(s) which in turnare affixed to the other element.

“Comprise,” “comprising,” and “comprises” are open ended terms, eachspecifies the presence of what follows, e.g., a component, but does notpreclude the presence of other features, e.g., elements, steps,components known in the art, or disclosed herein. These terms based onthe verb “comprise” should be read as encompassing the narrower terms“consisting of” which excludes any element, step, or ingredient notspecified and “consisting essentially of” which limits the scope of anelement to the specified materials or steps and those that do notmaterially affect the way the element performs its function. Anypreferred or exemplary embodiments described below are not limiting thescope of the claims, unless specifically indicated to do so. The words“typically”, “normally”, “advantageously” and the likes also qualifyelements which are not intended to limit the scope of the claims unlessspecifically indicated to do so.

General Description of the Absorbent Core 28

The absorbent core of the invention will be typically made to be used inan absorbent article of the type indicated before. The absorbent coremay for example be made on-line and assembled directly with theremaining components of the article or may be off-line at another siteand transported to the converting line. It is also possible to use theabsorbent core directly as an absorbent article without furtherassembling of other components for applications which do not requireother layers. Typically however the absorbent core will be assembledwith other components such as a topsheet and a backsheet to form afinished hygiene article, as will be exemplary described further belowfor a diaper.

The absorbent core is typically the component of the article having themost absorbent capacity. The absorbent core of the invention comprises acore wrap enclosing an absorbent material, and may also comprise atleast one adhesive. The absorbent material comprises a superabsorbentpolymer in particulate forms (herein abbreviated as “SAP”). Theabsorbent material may comprise relatively high amount of SAP enclosedwithin the core wrap. By “absorbent material” it is meant a materialwhich has some absorbency property or liquid retaining properties, suchas SAP, cellulosic fibers as well as synthetic fibers. Typically,adhesives used in making absorbent cores have no absorbency propertiesand are not considered as absorbent material.

The SAP content may represent at least 70% or more (in particular atleast 80%, at least 85%, at least 90%, at least 95% and up to 100%) byweight of the absorbent material enclosed in the core wrap. The corewrap itself is not considered as absorbent material for the purpose ofassessing the percentage of SAP in the absorbent core. High amount ofSAP provides a relatively thin core compared to conventional coretypically comprising between 40-60% by weight of cellulose fibers. Theabsorbent core may be thin, for example having a thickness not exceeding5 mm, e.g. from 0.2 mm to 4 mm, in particular from 0.5 to 3 mm, asmeasured with the Dry Absorbent Core Caliper Test disclosed therein.

An exemplary absorbent core 28 of the invention is shown in isolation inFIGS. 1-4 and will now be further described. The absorbent core shownand its description are purely for exemplary purpose and are notintended to limit the scope of the claims, unless otherwise stated. Theabsorbent core typically comprises a front side 280, a back side 282 andtwo longitudinal sides 284, 286 joining the front side 280 and the backside 282. The absorbent core also comprises a generally planar top side16 and a generally planar bottom side 16′ formed by the core wrap. Thefront side 280 of the core is the side of the core intended to be placedtowards the front edge 10 of the absorbent article. The core may have alongitudinal axis 80′ corresponding substantially to the longitudinalaxis of the article 80, as seen from the top in a planar view as inFIG. 1. Typically the absorbent material will be advantageouslydistributed in higher amount towards the front side and middle portionof the core than towards the back side as more absorbency is required atthe front. Typically the front and back sides of the core are shorterthan the longitudinal sides of the core. The core wrap may be formed bytwo nonwoven material which may be at least partially sealed along thesides of the absorbent core. The first nonwoven may substantially formthe whole of the top side of the core wrap and the second nonwovensubstantially the whole of the bottom side 16′ of the core wrap. The topside and first nonwoven are represented by the same number 16 on thedrawings, the bottom side and the second nonwoven by number 16′. Thecore wrap may be at least partially sealed along its front side, backside and/or two longitudinal sides to improve the containment of theabsorbent material during use.

The absorbent material may in particular comprises less than 10% weightpercent of natural or synthetic fibers, or less than 5% weight percent,or even be substantially free of natural and/or synthetic fibers. Theabsorbent material may advantageously comprise little or no airfelt(cellulose) fibers, in particular the absorbent core may comprise lessthan 15%, 10%, 5% airfelt (cellulose) fibers by weight of the absorbentcore, or even be substantially free of cellulose fibers.

Various absorbent core designs comprising high amount of SAP have beenproposed in the past, see for example in U.S. Pat. No. 5,599,335(Goldman), EP1,447,066 (Busam), WO95/11652 (Tanzer), US2008/0312622A1(Hundorf), WO2012/052172 (Van Malderen) and WO2012/170778 (Rosati etal., see also WO2012/170779, WO2012/170781 and WO2012/170808).

The absorbent core 28 comprises at least one area 26 which issubstantially free of absorbent material and through which the top sideof the core wrap is attached to the bottom side of the core wrap. Whenthe absorbent material absorbs a liquid, it swells in proportion and thecore wrap gradually forms a channel 26′ along the bonded area 26substantially free of absorbent material.

The length L″ of the absorbent core as measured along it axis 80′ fromthe front side 280 to the back side 282 should be adapted for theintended article in which it will be used. For infant diapers, thelength L″ may for example range from 5 to 40 cm. The absorbent corecomprises a crotch point C′ defined as the point on the longitudinalaxis 80′ situated at a distance of two fifth (⅖) of L″ starting from thefront side 280 of the absorbent core. The individual components of theabsorbent core will now be described in further details.

Core Wrap (16, 16′)

The function of the core wrap is to enclose the absorbent material.Typical core wraps comprise two substrates 16, 16′ which are attached toanother, but the core wrap may also be made of a single substrate foldedaround the absorbent material, or may comprises several substrates. Whentwo substrates are used, these may be typically attached to anotheralong at least part of the periphery of the absorbent core. Typicalattachments are the so-called C-wrap and sandwich wrap. In a C-wrap, asexemplarily shown in FIG. 2, the longitudinal and/or transversal edgesof one of the substrate are folded over the other substrate to formflaps. These flaps are then bonded to the external surface of the othersubstrate, typically by gluing. In a sandwich wrap, as shown on FIG. 3,the edges of both substrates are attached, e.g. by gluing, to another ina flat configuration.

The core wrap may be formed by any materials suitable for enclosing theabsorbent material. Typical substrate materials used in the productionof conventional cores may be used, in particular nonwovens but alsopaper, tissues, films, wovens, or laminate of any of these. The corewrap may in particular be formed by a nonwoven web, such as a cardednonwoven, a spunbond nonwoven (“S”) or a meltblown nonwoven (“M”), andlaminates of any of these. For example spunmelt polypropylene nonwovensare suitable, in particular those having a laminate web SMS, or SMMS, orSSMMS, structure, and having a basis weight range of about 5 gsm to 15gsm. Suitable materials are for example disclosed in U.S. Pat. No.7,744,576, US2011/0268932A1, US2011/0319848A1 or US2011/0250413A1.Nonwoven materials provided from synthetic fibers may be used, such asPE, PET and in particular PP.

If the core wrap comprises a first substrate 16 and a second substrate16′ these may be made of the same type of material, or may be made ofdifferent materials or one of the substrate may be treated differentlythan the other to provide it with different properties. As the polymersused for nonwoven production are inherently hydrophobic, they arepreferably coated with hydrophilic coatings if placed on the fluidreceiving side of the absorbent core. It is advantageous that the topside 16 of the core wrap, i.e. the side placed closer to the wearer inthe absorbent article, be more hydrophilic than the bottom side 16′ ofthe core wrap. A possible way to produce nonwovens with durablyhydrophilic coatings is via applying a hydrophilic monomer and a radicalpolymerization initiator onto the nonwoven, and conducting apolymerization activated via UV light resulting in monomer chemicallybound to the surface of the nonwoven. An alternative possible way toproduce nonwovens with durably hydrophilic coatings is to coat thenonwoven with hydrophilic nanoparticles, e.g. as described in WO02/064877.

Permanently hydrophilic nonwovens are also useful in some embodiments.Surface tension can be used to measure how permanently a certainhydrophilicity level is achieved. Liquid strike through can be used tomeasure the hydrophilicity level. The first and/or second substrate mayin particular have a surface tension of at least 55, preferably at least60 and most preferably at least 65 mN/m or higher when being wetted withsaline solution. The substrate may also have a liquid strike throughtime of less than 5 seconds for a fifth gush of liquid. These values canbe measured using the test methods described in U.S. Pat. No.7,744,576B2 (Busam et al.): “Determination Of Surface Tension” and“Determination of Strike Through” respectively.

Hydrophilicity and wettability are typically defined in terms of contactangle and the strike through time of the fluids, for example through anonwoven fabric. This is discussed in detail in the American ChemicalSociety publication entitled “Contact angle, wettability and adhesion”,edited by Robert F. Gould (Copyright 1964). A substrate having a lowercontact angle between the water and the surface of substrate may be saidto be more hydrophilic than another.

The substrates may also be air-permeable. Films useful herein maytherefore comprise micro-pores. The substrate may have for example anair-permeability of from 40 or from 50, to 300 or to 200 m³/(m²×min), asdetermined by EDANA method 140-1-99 (125 Pa, 38.3 cm²). The material ofthe core wrap may alternatively have a lower air-permeability, e.g.being non-air-permeable, for example to facilitate handling on a movingsurface comprising vacuum.

The core wrap may be sealed along its longitudinal edges and/or itstransversal edges. In a C-wrap configuration, for example, a firstsubstrate 16 may be placed on one side of the core and extends aroundthe core's longitudinal edges to partially wrap the opposed bottom sideof the core (see FIG. 2). The second substrate 16′ is typically presentbetween the wrapped flaps of the first substrate 16 and the absorbentmaterial 60. The flaps of the first substrate 16 may be glued to thesecond substrate 16′ to provide a strong seal. This so called C-wrapconstruction can provide benefits such as improved resistance tobursting in a wet loaded state compared to a sandwich seal. The frontside and back side of the core wrap may then also be sealed for exampleby gluing the first substrate and second substrate to another to providecomplete enclosing of the absorbent material across the whole of theperiphery of the core. For the front side and back side of the core thefirst and second substrate may extend and be joined together in asubstantially planar direction, forming for these edges a so-calledsandwich construction. In the so-called sandwich construction, the firstand second substrates may also extend outwardly on all sides of the coreand be sealed flat along the whole or parts of the periphery of the coretypically by gluing and/or heat/pressure bonding. Typically neitherfirst nor second substrates need to be shaped, so that they can berectangularly cut for ease of production but of course other shapes arepossible.

The terms “seal” and “enclosing” are to be understood in a broad sense.The seal does not need to be continuous along the whole periphery of thecore wrap but may be discontinuous along part or the whole of it, suchas formed by a series of seal points spaced on a line. Typically a sealmay be formed by gluing and/or thermal bonding. The core wrap may alsobe formed by a single substrate which may enclose the absorbent materialas in a parcel wrap and be for example sealed along the front side andback side of the core and one longitudinal seal.

Absorbent Material 60

The absorbent core 28 comprises an absorbent material 60 comprisingsuperabsorbent polymer particles (“SAP”). The absorbent material may befor example applied as a continuous layer. The absorbent material mayalso be comprised of individual pockets or stripes of absorbent materialenclosed within the core wrap. A continuous layer of absorbent material,in particular of SAP, may also be obtained by combining two absorbentlayers having matching discontinuous absorbent material applicationpattern wherein the resulting layer is substantially continuouslydistributed across the absorbent particulate polymer material area, astaught in US2008/0312622A1 (Hundorf) for example. In this way, eachabsorbent material layer comprises a pattern having absorbent materialareas and absorbent material-free areas, wherein the absorbent materialareas of the first layer correspond substantially to the absorbentmaterial-free areas of the second layer and vice versa. A microfibrousglue 51 as disclosed further below may be applied on each absorbentmaterial layer to immobilize it on each substrate. As exemplary shown inFIGS. 3-4, the absorbent core 28 may thus comprise a first absorbentlayer and a second absorbent layer, the first absorbent layer comprisinga first substrate 16 and a first layer 61 of absorbent material, whichmay be 100% SAP, and the second absorbent layer comprising a secondsubstrate 16′ and a second layer 62 of absorbent material, which mayalso be 100% SAP. The first and second SAP layers may be applied astransversal stripes or “land areas” having the same width as the desiredabsorbent material deposition area 8 on their respective substratebefore being combined. The stripes may advantageously comprise differentamount of absorbent material to provide a profiled basis weight alongthe longitudinal axis and/or transversal axis of the core 80′. The firstsubstrate 16 and the second substrate 16′ may form the core wrap. Anauxiliary glue 71, 72 may be applied between one or both substrates andthe absorbent layers, as well as microfiber glue on each absorbentlayer.

Superabsorbent Polymer Particles (SAP)

“Superabsorbent polymers” as used herein refer to absorbent materialwhich are cross-linked polymeric materials that can absorb at least 10times their weight of an aqueous 0.9% saline solution as measured usingthe Centrifuge Retention Capacity (CRC) test (EDANA method WSP241.2-05E). These polymers are typically used in particulate forms(“SAP”) so as to be flowable in the dry state. The term “particles”refers to granules, fibers, flakes, spheres, powders, platelets andother shapes and forms known to persons skilled in the art ofsuperabsorbent polymer particles.

Typical particulate absorbent polymer materials are made ofpoly(meth)acrylic acid polymers. However, e.g. starch-based particulateabsorbent polymer material may also be used, as well polyacrylamidecopolymer, ethylene maleic anhydride copolymer, cross-linkedcarboxymethylcellulose, polyvinyl alcohol copolymers, cross-linkedpolyethylene oxide, and starch grafted copolymer of polyacrylonitrile.The superabsorbent polymer may be polyacrylates and polyacrylic acidpolymers that are internally and/or surface cross-linked. Thesuperabsorbent polymers can be internally cross-linked, i.e. thepolymerization is carried out in the presence of compounds having two ormore polymerizable groups which can be free-radically copolymerized intothe polymer network. Exemplary superabsorbent polymer particles of theprior art are for example described in WO2006/083584, WO2007/047598,WO2007/046052, WO2009/155265, WO2009/155264.

Although it can be expected that SAP should experience a reduction inabsorption speed beyond the first gush as the core becomes loaded, theinventors have found that this reduction was significantly moreimportant in a core comprising channels compared to a similar corewithout channels. The present invention uses SAP having a time to reachan uptake of 20 g/g (T20) of less than 240 s as measured by the K(t)test method described in WO2012/174026A1 to solve this problem. The SAPmay in particular have a T20 of less than 220 s, or less than 200 s, orless than 180 s, or less than 160 s. The time T20 may also be inparticular of at least of 40 s, 60 s, 80 s, 100 s, 120 s or 140 s andany combinations of these values to form a range, e.g. of from 100 s to200 s. WO2012/174,026A1 describes SAP having these properties and themethod used to measure these parameters. An equipment used for thismethod is called ‘Zeitabhängiger Durchlässigkeitspriffstand’ or ‘TimeDependent Permeability Tester’, Equipment No. 03-080578 and iscommercially available at BRAUN GmbH, Frankfurter Str. 145, 61476Kronberg, Germany and is detailed in the above mentioned application.Upon request, operating instructions, wiring diagrams and detailedtechnical drawings are also available.

The K(t) method is also useful to determine other SAP parameters, whichmay also be advantageously used in the present invention. The uptake ofthe SAP at 20 min (U20) may be in particular of at least 22 g/g, or atleast 24 g/g, or at least 28 g/g or at least 30 g/g, or of from 28 g/gto 60 g/g, or of from 30 g/g to 50 g/g, or of from 30 g/g to 40 g/g asmeasured according to the K(t) test method disclosed inWO2012/174,026A1. The SAP may have an effective permeability at 20minutes (K20) of at least 5·10⁻⁸ cm², or at least 7·10⁻⁸ cm², or atleast 8.5·10⁻⁸ cm², or of 5·10⁻⁸ cm² to 1·10⁻⁶ cm², or of 7·10⁻⁸ cm² to5·10⁻⁷ cm², or of 8.5·10⁻⁸ to 1·10⁻⁷ cm² as measured according to theK(t) test method.

The SAP may also have a ratio between the minimum effective permeabilityand the permeability at 20 minutes (Kmin/K20 ratio) of more than 0.75,or more than 0.8 or more than 0.9 as measured according to the K(t) testmethod. In such embodiments the transient gel blocking is minimum andthe liquid exudates are able to travel fast through the void spacespresent between the particles throughout all the swelling process andespecially in the initial part of the swelling phase which is the mostcritical for the first gush.

For embodiments having more than one type of superabsorbent polymerparticles, the K(t) test method is carried out on a mixture of the morethan one type of superabsorbent polymer particles present in theirrespective proportion as used in the absorbent core.

The superabsorbent polymer particles may further have a permeability atequilibrium expressed as UPM (Urine Permeability Measurement) value ofmore than 40, or preferably more than 50, or more than 60, or of 50 to500, or of 55 to 200, or of 60 to 150 UPM units, where 1 UPM unit is1×10⁻⁷ (cm³·s)/g. The UPM value is measured according to the UPM Testmethod set out in WO2012/174,026A1. This method is closely related tothe SFC test method of the prior art. The UPM Test method typicallymeasures the flow resistance of a preswollen layer of superabsorbentpolymer particles, i.e. the flow resistance is measured at equilibrium.Therefore, such superabsorbent polymer particles having a high UPM valueexhibit a high permeability when a significant volume of the absorbentarticle is already wetted by the liquid exudates. These embodimentsexhibit good absorption properties not only at the first gush but alsoat the subsequent gushes.

The SAP used may also have a FSR (Free Swell Rate) of more than 0.1g/g/s, or of from 0.1 to 2 g/g/s, or 0.3 to 1 g/g/s, or 0.3 to 0.6g/g/s, or 0.4 to 0.6 g/g/s. The Free Swell Rate of the SAP is measuredaccording to the FSR test method set out in WO2012/174,026A1. SAP havinghigh free swell rate values will be able to absorb liquid quickly underno confining pressure. Contrary to the K(t) test method, no externalpressure is applied to the gel bed in order to measure the free swellrate. SAP having a too low FSR value may require more than 240 s toreach an uptake of 20 g/g as measured according to the K(t) test methodof the present invention and will consequently not be able to absorb theliquid exudates as fast as necessary. However, as stated above,superabsorbent polymer particles having a high FSR value do notautomatically lead to high uptake values as measured according to theK(t) test method.

The SAP may have a CRC (centrifuge retention capacity) value of morethan 18 g/g, or more than 20 g/g, or more than 22 g/g, or more than 24g/g, for example up to 50 g/g, or up to 40 g/g, or to 30 g/g, asmeasured according to EDANA method WSP 241.2-05. The CRC measures theliquid absorbed by the superabsorbent polymer particles for freeswelling in excess liquid. Superabsorbent polymer particles having ahigh CRC value may be preferred since less superabsorbent polymerparticles are needed to facilitate a required overall capacity forliquid absorption.

At least some of the superabsorbent polymers may be present in the formof agglomerated superabsorbent polymer particles. Agglomeratedsuperabsorbent polymer particles comprise agglomerated precursorparticles having a first mass average particle size, and wherein theagglomerated superabsorbent polymer particles have a second mass averageparticle size which is at least 25% greater than the first mass averageparticle size. The second mass average particle size may be at least30%, or at least 40% or at least 50% higher than the first mass averageparticle size. Mass average particle size may be measured according toMass Average Particle Size Sieve Test method described below.

The agglomerated superabsorbent polymer particles may be obtained byvarious methods. Agglomerated particles may be for example obtained byaggregating the precursor particles with an interparticle crosslinkingagent reacted with the polymer material of the precursor particles toform crosslink bonds between the precursor particles have been forexample disclosed in U.S. Pat. No. 5,300,565, U.S. Pat. No. 5,180,622,(both to Berg), U.S. Pat. No. 5,149,334, U.S. Pat. No. 5,102,597 (bothto Roe), U.S. Pat. No. 5,492,962 (Lahrman). Agglomerated superabsorbentpolymer particles may also be obtained by a method comprising the stepsof providing superabsorbent polymer particles and mixing thesuperabsorbent polymer particles with a solution comprising water and amultivalent salt having a valence of three or higher. This method isfurther disclosed in co-pending application number EP14168064.

The superabsorbent polymer particles of the core of the invention may inparticular comprise at least 10%, or at least 20% or at least 30% or atleast 50% by weight of the agglomerated superabsorbent polymer particles

The total amount of SAP present in the absorbent core may also varyaccording to expected user of the article. Diapers for newborns requireless SAP than infant or adult incontinence diapers. The amount of SAP inthe core may be for example comprised from about 2 to 50 g, inparticular from 5 to 40 g for typical enfant diapers. The average SAPbasis weight within the (or “at least one”, if several are present)deposition area 8 of the SAP may be for example of at least 50, 100,200, 300, 400, 500 or more g/m². The material free areas 26 present inthe absorbent material deposition area 8 are deduced from the absorbentmaterial deposition area to calculate this average basis weight.

Area(s) 26 Substantially Free of Absorbent Material and Channels 26′

The absorbent core 28 comprises one or more area(s) 26 which is/aresubstantially free of absorbent material. By “substantially free” it ismeant that in each of these areas the basis weight of the absorbentmaterial is at least less than 25%, in particular less than 20%, lessthan 10%, of the average basis weight of the absorbent material in therest of the core. In particular there can be no absorbent material inthese areas. Minimal amount such as involuntary contaminations withabsorbent material that may occur during the making process are notconsidered as absorbent material. The areas 26 are advantageouslysurrounded by the absorbent material, when seen in the plane of thecore, which means that the area(s) 26 does not extend to any of the edgeof the deposition area 8 of the absorbent material.

The top side 16 of the core wrap is attached to the bottom side 16′ ofthe core wrap by core wrap bond(s) 27 through these area(s) 26substantially free of absorbent material. As shown in FIG. 7, when theabsorbent material swells upon absorbing a liquid, the core wrap bondremains at least initially attached in the substantially material freearea(s) 26. The absorbent material swells in the rest of the core whenit absorbs a liquid, so that the core wrap forms one or more channel(s)26′ along the area(s) 26 substantially free of absorbent materialcomprising the core wrap bond 27. These channels 26′ are threedimensional and can serve to distribute an insulting fluid along theirlength to a wider area of the core. This may provide a quicker fluidacquisition speed and a better utilization of the absorbent capacity ofthe core. The channels 26′ can also provide a deformation of anoverlying layer such as a fibrous layer 54 and provide correspondingditches 29 in the overlying layer. It is not excluded that the absorbentcore may comprise other area(s) substantially free of absorbent materialbut without a core wrap bond, but these non-bonded areas will typicallynot form a channel when wet.

The top side 16 and the bottom side 16′ of the core wrap may be attachedtogether continuously along the area(s) 26 substantially free ofabsorbent material, but the core wrap bond 27 may also be discontinuous(intermittent) such as series of point bonds. Typically, an adhesive canbe used to attach the top side to the bottom of the core wrap, but it ispossible to bond via other known attachment means, such as pressurebonding, ultrasonic bonding or heat bonding or combination thereof. Theattachment of the top side and bottom side of the core wrap may beprovided by one or more adhesive material, in particular one or morelayers of auxiliary glue 71, 72 and/or one or more layers of fibrousadhesive material 51, if present in the core, as indicated below. Theseglues may therefore serve the dual function of immobilizing theabsorbent material and attach the top side and the bottom side of thecore together.

The following examples of the shape and size of the areas 26substantially free of absorbent material are not limiting. In general,the core wrap bond 27 may have the same outline but be slightly smallerthan the areas 26 due to the tolerance required in some manufacturingprocess. The substantially material free area(s) 26 may be presentwithin the crotch region of the article, in particular at least at thesame longitudinal level as the crotch point C′, as represented in FIG. 1by the two longitudinally extending areas substantially free ofabsorbent material 26. The absorbent core 28 may also comprise more thantwo substantially absorbent material free area(s), for example at least3, or at least 4 or at least 5 or at least 6. The absorbent core maycomprise one or more pairs of areas substantially free of absorbentmaterial symmetrically arranged relative to the longitudinal axis 80′.Shorter area(s) substantially free of absorbent material may also bepresent, for example in the back region or the front region of the core,as seen for example in the Figures of WO2012/170778.

The area(s) 26 substantially free of absorbent material may extendsubstantially longitudinally, which means typically that each areaextends more in the longitudinal direction than in the transversedirection, and typically at least twice as much in the longitudinaldirection than in the transverse direction (as measured after projectionon the respective axis). The area(s) 26 substantially free of absorbentmaterial may have a length L′ projected on the longitudinal axis 80′ ofthe core that is at least 10% of the length L″ of the absorbent core, inparticular from 20% to 80%. It may be advantageous that at least some orall of the area(s) 26 are not completely or substantially completelytransversely oriented channels in the core.

The area(s) 26 substantially free of absorbent material may becompletely oriented longitudinally and parallel to the longitudinal axisbut also may be curved. In particular some or all these area(s), inparticular these area(s) present in the crotch region, may be concavetowards the longitudinal axis 80′, as for example represented in FIG. 1for the pair of channels 26′. The radius of curvature may typically beat least equal (and preferably at least 1.5 or at least 2.0 times thisaverage transverse dimension) to the average transverse dimension of theabsorbent material deposition area 8; and also straight but under anangle of (e.g. from 5°) up to 30°, or for example up to 20°, or up to10° with a line parallel to the longitudinal axis. The radius ofcurvature may be constant for a substantially absorbent material freearea(s), or may vary along its length. This may also includes area(s)substantially free of absorbent material with an angle therein, providedsaid angle between two parts of a channel is at least 120°, preferablyat least 150°; and in any of these cases, provided the longitudinalextension of the area is more than the transverse extension. Thesearea(s) may also be branched, for example a central substantiallymaterial free area superposed with the longitudinal axis in the crotchregion which branches towards the back and/or towards the front of thearticle.

In some embodiments, there is no area(s) substantially free of absorbentmaterial that coincides with the longitudinal axis 80′ of the core. Whenpresent as one ore symmetrical pair(s) relative to the longitudinalaxis, the area(s) substantially free of absorbent material may be spacedapart from one another over their whole longitudinal dimension. Thesmallest spacing distance may be for example at least 5 mm, or at least10 mm, or at least 16 mm.

Furthermore, in order to reduce the risk of fluid leakages, the area(s)substantially free of absorbent material may advantageously not extendup to any of the edges of the absorbent material deposition area 8, andare therefore surrounded by and fully encompassed within the absorbentmaterial deposition area 8 of the core. Typically, the smallest distancebetween an area(s) substantially free of absorbent material and theclosest edge of the absorbent material deposition area is at least 5 mm.

The area(s) substantially free of absorbent material may have a width Wcalong at least part of its length which is at least 2 mm, or at least 3mm or at least 4 mm, up to for example 20 mm, or 16 mm or 12 mm. Thewidth Wc of the area(s) substantially free of absorbent material may beconstant through substantially its whole length or may vary along itslength.

The channels 26′ in the absorbent core start forming when the absorbentmaterial absorbs a liquid such as urine and starts swelling. As the coreabsorbs more liquid, the depressions within the absorbent core formed bychannels will become deeper and more apparent to the eye and the touch.It is possible to create a sufficiently strong core wrap bond combinedwith a relatively low amount of SAP so that the channels remainpermanent until complete saturation of the absorbent material. On theother hand, the core wrap bonds may in some cases also restrict theswelling of the absorbent material when the core is substantiallyloaded. The inventors have thus found that the core wrap bond 27 mayalso be designed to open in a controlled manner when exposed to a largeamount of fluid. The bonds may thus remain substantially intact at leastduring a first phase as the absorbent material absorbs a moderatequantity of fluid. In a second phase the core wrap bonds 27 in thechannels can start opening to provide more space for the absorbentmaterial to swell while keeping most of the benefits of the channelssuch as increased flexibility of the core in transversal direction andfluid management. In a third phase, corresponding to a very highsaturation of the absorbent core, a more substantial part of the channelbonds can open to provide even more space for the swelling absorbentmaterial to expand. The strength of core wrap bond 27 within thechannels can be controlled for example by varying the amount and natureof the glue used for the attaching the two sides of the core wrap, thepressure used to make the core wrap bond and/or the distribution of theabsorbent material, as more absorbent material will usually causes moreswelling and will put more pressure on the bond. The extensibility ofthe material of the core wrap may also play a role.

Absorbent Material Deposition Area 8

The absorbent material deposition area 8 can be defined by the peripheryof the layer formed by the absorbent material 60 within the core wrap,as seen from the top side of the absorbent core. The absorbent materialdeposition area 8 can be generally rectangular, for example as shown inFIG. 1, but other shapes can also be used such as a “T” or “Y” or“sand-hour” or “dog-bone” shape. In particular the deposition area maywhich show a tapering along its width towards the middle or “crotch”region of the core. In this way, the absorbent material deposition areamay have a relatively narrow width in an area of the core intended to beplaced in the crotch region of the absorbent article. This may providefor example better wearing comfort. The absorbent material depositionarea 8 may thus have a width (as measured in the transversal direction)at its narrowest point which is less than about 100 mm, 90 mm, 80 mm, 70mm, 60 mm or even less than about 50 mm. This narrowest width mayfurther be for example at least 5 mm, or at least 10 mm, smaller thanthe width of the deposition area at its largest point in the frontand/or back regions of the deposition area 8.

The basis weight (amount deposited per unit of surface) of the SAP mayalso be varied along the deposition area 8 to create a profileddistribution of absorbent material, in particular SAP, in thelongitudinal direction (as shown in FIG. 3), in the transversaldirection, or both directions of the core. Hence along the longitudinalaxis of the core, the basis weight of absorbent material may vary, aswell as along the transversal axis, or any axis parallel to any of theseaxes. The basis weight of SAP in area of relatively high basis weightmay thus be for example at least 10%, or 20%, or 30%, or 40%, or 50%higher than in an area of relatively low basis weight. In particular theSAP present in the absorbent material deposition area at thelongitudinal position of the crotch point C′ may have more SAP per unitof surface deposited as compared to another area of the absorbentmaterial deposition area 8.

The absorbent material may be deposited using known techniques, whichmay allow relatively precise deposition of SAP at relatively high speed.In particular the SAP printing technology as disclosed for example inUS2006/024433 (Blessing), US2008/0312617 and US2010/0051166A1 (both toHundorf et al.) may be used. This technique uses a transfer device suchas a printing roll to deposit SAP onto a substrate disposed on a grid ofa support which may include a plurality of cross bars extendingsubstantially parallel to and spaced from one another so as to formchannels extending between the plurality of cross-bars. This technologyallows high-speed and precise deposition of SAP on a substrate inparticular to provide one or more area(s) 26 substantially free ofabsorbent material surrounded by absorbent material. The areassubstantially free of absorbent material can be formed for example bymodifying the pattern of the grid and receiving drums so that no SAP isapplied in the selected areas, as exemplary disclosed in US2012/0312491(Jackels).

Microfiber Glue 51

The absorbent core may also comprise a fibrous thermoplastic adhesivematerial 51, in particular a microfiber glue, to further immobilize theabsorbent material within the core. The fibrous thermoplastic adhesivematerial 51 may be useful to immobilize the layer of absorbent materials61, 62 to their respective substrate, in particular when the absorbentlayer(s) comprises land areas separated by junction areas. The fibrousthermoplastic adhesive material 51 may then be at least partially incontact with the absorbent material 61, 62 in the land areas and atleast partially in contact with the substrate layer 16, 16′ in thejunction areas. This imparts an essentially three-dimensional net-likestructure to the fibrous layer of thermoplastic adhesive material 51,which in itself is essentially a two-dimensional structure of relativelysmall thickness, as compared to the dimension in length and widthdirections. Thereby, the fibrous thermoplastic adhesive material mayprovide cavities to cover the absorbent material in the land areas, andthereby immobilizes this absorbent material. The microfiber glue 51 maybe for example applied by spraying each absorbent layer.

The thermoplastic polymer may typically have a molecular weight (Mw) ofmore than 10,000 and a glass transition temperature (Tg) usually belowroom temperature or −6° C.<Tg<16° C. Typical concentrations of thepolymer in a hotmelt are in the range of about 20 to about 40% byweight. The thermoplastic polymers may be water insensitive. Exemplarypolymers are (styrenic) block copolymers including A-B-A triblockstructures, A-B diblock structures and (A-B)n radial block copolymerstructures wherein the A blocks are non-elastomeric polymer blocks,typically comprising polystyrene, and the B blocks are unsaturatedconjugated diene or (partly) hydrogenated versions of such. The B blockis typically isoprene, butadiene, ethylene/butylene (hydrogenatedbutadiene), ethylene/propylene (hydrogenated isoprene), and mixturesthereof. Other suitable thermoplastic polymers that may be employed aremetallocene polyolefins, which are ethylene polymers prepared usingsingle-site or metallocene catalysts. Therein, at least one comonomercan be polymerized with ethylene to make a copolymer, terpolymer orhigher order polymer. Also applicable are amorphous polyolefins oramorphous polyalphaolefins (APAO) which are homopolymers, copolymers orterpolymers of C2 to C8 alpha olefins.

The tackifying resin may exemplarily have a Mw below 5,000 and a Tgusually above room temperature, typical concentrations of the resin in ahotmelt are in the range of about 30 to about 60%, and the plasticizerhas a low Mw of typically less than 1,000 and a Tg below roomtemperature, with a typical concentration of about 0 to about 15%.

The thermoplastic adhesive used for the fibrous layer preferably haselastomeric properties, such that the web formed by the fibers on theSAP layer is able to be stretched as the SAP swell. Exemplaryelastomeric, hotmelt adhesives include thermoplastic elastomers such asethylene vinyl acetates, polyurethanes, polyolefin blends of a hardcomponent (generally a crystalline polyolefin such as polypropylene orpolyethylene) and a Soft component (such as ethylene-propylene rubber);copolyesters such as poly (ethylene terephthalate-co-ethylene azelate);and thermoplastic elastomeric block copolymers having thermoplastic endblocks and rubbery mid blocks designated as A-B-A block copolymers:mixtures of structurally different homopolymers or copolymers, e.g., amixture of polyethylene or polystyrene with an A-B-A block copolymer;mixtures of a thermoplastic elastomer and a low molecular weight resinmodifier, e.g., a mixture of a styrene-isoprenestyrene block copolymerwith polystyrene; and the elastomeric, hot-melt, pressure-sensitiveadhesives described herein. Elastomeric, hot-melt adhesives of thesetypes are described in more detail in U.S. Pat. No. 4,731,066 (Korpman).

The thermoplastic adhesive material 51 fibers may exemplarily have anaverage thickness of about 1 to about 50 micrometers or about 1 to about35 micrometers and an average length of about 5 mm to about 50 mm orabout 5 mm to about 30 mm. To improve the adhesion of the thermoplasticadhesive material to the substrate or to any other layer, in particularany other nonwoven layer, such layers may be pre-treated with anauxiliary adhesive. The fibers adhere to each other to form a fibrouslayer, which can also be described as a mesh.

The absorbent core advantageously achieve an SAP loss of no more thanabout 70%, 60%, 50%, 40%, 30%, 20%, 10% according to the WetImmobilization Test described in US2010/0051166A1.

Auxiliary Glue 71, 72

The absorbent core of the invention may further comprise an auxiliaryglue present on the inner surface of the top side and/bottom side of theabsorbent core, in particular to help immobilizing the SAP within thecore wrap, to ensure integrity of the core wrap and/or to form the bond27 attaching the bottom side of the core wrap to the top side of thecore wrap through the one or more area(s) substantially free ofabsorbent material.

This so-called auxiliary glue 71, 72 can be applied on the inner surfaceof the top side and/or the bottom side of the core wrap. The auxiliaryglue may be any conventional glue used in the field, in particularhotmelt glue. Example of glues are based on an adhesive polymer such SIS(Styrene-Isoprene-Block Co-Polymer), SBS (Styrene-Butadiene-BlockCo-polymer) or mPO (metalocine Polyolefine). The glue may also comprisea tackifier such as a hydrogenated hydrocarbon resin, as well as an oiland an antioxidant. Hydrogenated hydrocarbon resins are made from mixedaromatic/aliphatic resins which are subsequently selectivelyhydrogenated to produce a wide range of materials with low color, highstability and broad compatibility. Examples of commercially availableadhesives are available as HL1358LO and NW1286 (both from HB Fuller) andDM 526 (from Henkel).

The auxiliary glue may be applied on the top side and/or the bottom sideof the core wrap in an average amount ranging from 2 gsm to 20 gsm, moreparticularly from 4 gsm to 10 gsm. The auxiliary glue may be uniformlyapplied, or discontinuously, in particular as a series of stripesregularly spaced and longitudinally oriented, for example a series ofauxiliary glue stripes of about 1 mm width spaced from each other by adistance raging from 1 mm to 3 mm. The auxiliary glue may help formingthe core wrap bond 27 if sufficient pressure and glue is applied withinthe material free area 26 to attach both sides of the core wrap. Theauxiliary glue layer may be applied to the inner surface of the bottomside, the inner surface of the top side, or both inner surfaces of thecore wrap.

General Description of the Absorbent Article

Having now discussed in quite details certain embodiments of theabsorbent cores of the invention, the absorbent articles in which thesecores may be used will now be generally discussed and furtherillustrated in the form of a baby diaper 20 in FIGS. 5-7. FIG. 5 is aplan view of the exemplary diaper 20, in a flattened state, withportions of the structure being cut-away to more clearly show theconstruction of the diaper 20. This diaper 20 is shown for illustrationpurpose only as the invention may be used for making a wide variety ofdiapers or other absorbent articles.

The absorbent article comprises a liquid permeable topsheet 24, a liquidimpermeable backsheet 25, and an absorbent core 28 between the topsheet24 and the backsheet 25. An optional acquisition/distribution layer 54is represented on FIG. 5, which also shows other typical taped diapercomponents such as a fastening system comprising adhesive tabs 42attached towards the back edge of the article and cooperating with alanding zone 44 on the front of the article, barrier leg cuffs 34 andelasticized gasketing cuffs 32 joined to the chassis of the absorbentarticle, typically via the topsheet and/or backsheet, and substantiallyplanar with the chassis of the diaper. The absorbent article may alsocomprise other typical elements, which are not represented, such as aback elastic waist feature, a front elastic waist feature, transversebarrier cuff(s), a lotion application, etc. . . . .

The absorbent article 20 comprises a front edge 10, a back edge 12, andtwo side (longitudinal edges) 13, 14. The front edge 10 of the articleis the edge which is intended to be placed towards the front of the userwhen worn, and the back edge 12 is the opposite edge of the article. Theabsorbent article may be notionally divided by a longitudinal axis 80extending from the front edge to the back edge of the article anddividing the article in two substantially symmetrical halves relative tothis axis, with article placed flat and viewed from above as in FIG. 5.The length L of the article can be measured along the longitudinal axis80 from front edge 10 to back edge 12. The article comprises a crotchpoint C defined herein as the point placed on the longitudinal axis at adistance of two fifth (⅖) of L starting from the front edge 10 of thearticle 20. The width of the article for a diaper application at thecrotch point may in particular be of from 50 mm to 300 mm, or from 80 mmto 250 mm. For adult incontinence products the width may go up to 450mm.

The crotch region can be defined as the region of the diaperlongitudinally centered at the crotch point C and extending towards thefront and towards the back of the absorbent article by a distance of onefifth of L (L/5) in each direction. A front region and a back region canbe defined as the remaining portions of the diapers placed respectivelytowards the front and the back edges of the article.

The topsheet 24, the backsheet 25, the absorbent core 28 and the otherarticle components may be assembled in a variety of well knownconfigurations, in particular by gluing or heat embossing. Exemplarydiaper configurations are described generally in U.S. Pat. No.3,860,003, U.S. Pat. No. 5,221,274, U.S. Pat. No. 5,554,145, U.S. Pat.No. 5,569,234, U.S. Pat. No. 5,580,411, and U.S. Pat. No. 6,004,306. Theabsorbent article is preferably thin. The caliper at the crotch point Cof the article may be for example from 3.0 mm to 12.0 mm, in particularfrom 4.0 mm to 10.0 mm, as measured with the Absorbent Article CaliperTest described herein.

For most absorbent articles, the liquid discharge occurs predominatelyin the front half of the article, in particular for diaper. The fronthalf of the article (as defined by the region between the front edge anda transversal line 90 placed at a distance of half L from the front orback edge may therefore comprise most of the absorbent capacity of thecore. Thus, at least 60% of the SAP, or at least 65%, 70%, 75% or 80% ofthe SAP may be present in the front half of the absorbent article, theremaining SAP being disposed in the back half of the absorbent article.

The absorbent article may have an acquisition time for the first gush ofless than 30 s, preferably less than 27 s, as measured according to theFlat Acquisition test method set out in WO2012/174026A1. Thisacquisition time may be in measured in particular on a baby diaper whichis designated for wearers having a weight in the range of 8 to 13 kg±20%(such as Pampers Active Fit size 4 or other Pampers baby diapers size 4,Huggies baby diapers size 4 or baby diapers size 4 of most othertradenames).

Topsheet 24

The topsheet 24 is the layer of the absorbent article that is destinedto be in contact with the wearer's skin. The topsheet 24 can be joinedto the backsheet 25, the core 28 and/or any other layers as is known inthe art. Usually, the topsheet 24 and the backsheet 25 may be joineddirectly to each other on or close to the periphery of the article andare indirectly joined together in other locations by directly joiningthem to one or more other elements of the article 20. The topsheet maybe attached to an underlying layer 54, which may be an acquisitionand/or distribution layer, by any conventional means, in particulargluing, mechanical or heat bonding and combinations thereof. Thetopsheet may in particular be attached directly or indirectly to thefibrous layer 54 in the area where the ditches of the fibrous layer areformed, as exemplarily shown in FIG. 7. This may provide or help theformation of secondary ditches 29 at the surface of the article.

The topsheet 24 is preferably compliant, soft-feeling, andnon-irritating to the wearer's skin. Further, at least a portion of thetopsheet 24 is liquid permeable, permitting liquids to readily penetratethrough its thickness. A suitable topsheet may be manufactured from awide range of materials, such as porous foams, reticulated foams,apertured plastic films, or woven or nonwoven materials of naturalfibers (e.g., wood or cotton fibers), synthetic fibers or filaments(e.g., polyester or polypropylene or bicomponent PE/PP fibers ormixtures thereof), or a combination of natural and synthetic fibers. Ifthe topsheet includes fibers, the fibers may be spunbond, carded,wet-laid, meltblown, hydroentangled, or otherwise processed as is knownin the art, in particular spunbond PP nonwoven. A suitable topsheetcomprising a web of staple-length polypropylene fibers is manufacturedby Veratec, Inc., a Division of International Paper Company, of Walpole,Mass. under the designation P-8.

Suitable formed film topsheets are also described in U.S. Pat. No.3,929,135, U.S. Pat. No. 4,324,246, U.S. Pat. No. 4,342,314, U.S. Pat.No. 4,463,045, and U.S. Pat. No. 5,006,394. Other suitable topsheets maybe made in accordance with U.S. Pat. Nos. 4,609,518 and 4,629,643 issuedto Curro et al. Such formed films are available from The Procter &Gamble Company of Cincinnati, Ohio as “DRI-WEAVE” and from TredegarCorporation, based in Richmond, Va., as “CLIFF-T”.

Any portion of the topsheet 24 may be coated with a lotion as is knownin the art. Examples of suitable lotions include those described in U.S.Pat. No. 5,607,760, U.S. Pat. No. 5,609,587, U.S. Pat. No. 5,635,191,U.S. Pat. No. 5,643,588, U.S. Pat. No. 5,968,025 and U.S. Pat. No.6,716,441. The topsheet 24 may also include or be treated withantibacterial agents, some examples of which are disclosed in PCTPublication WO95/24173. Further, the topsheet 24, the backsheet 25 orany portion of the topsheet or backsheet may be embossed and/or mattefinished to provide a more cloth like appearance.

The topsheet 24 may comprise one or more apertures to ease penetrationof exudates therethrough, such as urine and/or feces (solid, semi-solid,or liquid). The size of at least the primary aperture is important inachieving the desired waste encapsulation performance. If the primaryaperture is too small, the waste may not pass through the aperture,either due to poor alignment of the waste source and the aperturelocation or due to fecal masses having a diameter greater than theaperture. If the aperture is too large, the area of skin that may becontaminated by “rewet” from the article is increased. Typically, thetotal area of the apertures at the surface of a diaper may have an areaof between about 10 cm² and about 50 cm², in particular between about 15cm² and 35 cm². Examples of apertured topsheet are disclosed in U.S.Pat. No. 6,632,504, assigned to BBA NONWOVENS SIMPSONVILLE.WO2011/163582 also discloses suitable colored topsheet having a basisweight of from 12 to 18 gsm and comprising a plurality of bonded points.Each of the bonded points has a surface area of from 2 mm² to 5 mm² andthe cumulated surface area of the plurality of bonded points is from 10to 25% of the total surface area of the topsheet.

Typical diaper topsheets have a basis weight of from about 10 to about28 gsm, in particular between from about 12 to about 18 gsm but otherbasis weights are possible.

Backsheet 25

The backsheet 25 is generally that portion of the absorbent article 20which forms the majority of the external surface of the article whenworn by the user. The backsheet is positioned towards the bottom side ofthe absorbent core and prevents the exudates absorbed and containedtherein from soiling articles such as bedsheets and undergarments. Thebacksheet 25 is typically impermeable to liquids (e.g. urine). Thebacksheet may for example be or comprise a thin plastic film such as athermoplastic film having a thickness of about 0.012 mm to about 0.051mm. Exemplary backsheet films include those manufactured by TredegarCorporation, based in Richmond, Va., and sold under the trade name CPC2film. Other suitable backsheet materials may include breathablematerials which permit vapors to escape from the diaper 20 while stillpreventing exudates from passing through the backsheet 25. Exemplarybreathable materials may include materials such as woven webs, nonwovenwebs, composite materials such as film-coated nonwoven webs, microporousfilms such as manufactured by Mitsui Toatsu Co., of Japan under thedesignation ESPOIR NO and by Tredegar Corporation of Richmond, Va., andsold under the designation EXAIRE, and monolithic films such asmanufactured by Clopay Corporation, Cincinnati, Ohio under the nameHYTREL blend P18-3097. Some breathable composite materials are describedin greater detail in PCT Application No. WO 95/16746 published on Jun.22, 1995 in the name of E. I. DuPont; U.S. Pat. No. 5,938,648 to LaVonet al., U.S. Pat. No. 4,681,793 to Linman et al., U.S. Pat. No.5,865,823 to Curro; and U.S. Pat. No. 5,571,096 to Dobrin et al, U.S.Pat. No. 6,946,585B2 to London Brown.

The backsheet 25 may be joined to the topsheet 24, the absorbent core 28or any other element of the diaper 20 by any attachment means known inthe art. Suitable attachment means are described above with respect tomeans for joining the topsheet 24 to other elements of the article 20.For example, the attachment means may include a uniform continuous layerof adhesive, a patterned layer of adhesive, or an array of separatelines, spirals, or spots of adhesive. Suitable attachment meanscomprises an open pattern network of filaments of adhesive as disclosedin U.S. Pat. No. 4,573,986. Other suitable attachment means includeseveral lines of adhesive filaments which are swirled into a spiralpattern, as is illustrated by the apparatus and methods shown in U.S.Pat. No. 3,911,173, U.S. Pat. No. 4,785,996; and U.S. Pat. No.4,842,666. Adhesives which have been found to be satisfactory aremanufactured by H. B. Fuller Company of St. Paul, Minn. and marketed asHL-1620 and HL 1358-XZP. Alternatively, the attachment means maycomprise heat bonds, pressure bonds, ultrasonic bonds, dynamicmechanical bonds, or any other suitable attachment means or combinationsof these attachment means as are known in the art.

Additional Layer 54

The absorbent article may further comprise one or more additional layer54 that can serve to acquire and distribute the fluid, as illustrate bylayer 54 in the Figures. The additional layer(s) may be present betweenthe topsheet 24 and the absorbent core 28, as represented in theFigures, but it may be also between the backsheet 25 and the absorbentcore 28, or both. The additional layer 54 may be at least partiallybonded to the top side or the bottom side of the core wrap in thearea(s) substantially free of absorbent material. The formation of thechannel 26′ in the absorbent core as the absorbent material swells maythus provides of one or more corresponding ditches 27 in the additionallayer 54.

The additional layer(s) may be of any kind such as nonwoven, a wovenmaterial or even loose fibers. The additional layers may in particularbe of the type known in the art for acquisition layers and/ordistribution layers. Typical acquisition and/or distribution layers donot comprise SAP as this may slow the acquisition and distribution ofthe fluid, but an additional layer may also comprise SAP if some fluidretention properties are wished. The prior art discloses many type ofacquisition and/or distribution layers that may be used, see for exampleWO2000/59430 (Daley), WO95/10996 (Richards), U.S. Pat. No. 5,700,254(McDowall), WO02/067809 (Graef).

A distribution layer can spread an insulting fluid liquid over a largersurface within the article so that the absorbent capacity of the corecan be more efficiently used. Typically distribution layers are made ofa nonwoven material based on synthetic or cellulosic fibers and having arelatively low density. The density of the distribution layer may varydepending on the compression of the article, but may typically rangefrom 0.03 to 0.25 g/cm³, in particular from 0.05 to 0.15 g/cm³ measuredat 0.30 psi (2.07 kPa). The distribution layer may also be a materialhaving a water retention value of from 25 to 60, preferably from 30 to45, measured as indicated in the procedure disclosed in U.S. Pat. No.5,137,537. The distribution layer may typically have an average basisweight of from 30 to 400 g/m², in particular from 100 to 300 g/m².

The distribution layer may for example comprise at least 50% by weightof cross-linked cellulose fibers. The cross-linked cellulosic fibers maybe crimped, twisted, or curled, or a combination thereof includingcrimped, twisted, and curled. This type of material has been used in thepast in disposable diapers as part of an acquisition system, for exampleUS 2008/0312622 A1 (Hundorf). The cross-linked cellulosic fibers providehigher resilience and therefore higher resistance to the first absorbentlayer against the compression in the product packaging or in useconditions, e.g. under a baby's weight. This provides the core with ahigher void volume, permeability and liquid absorption, and hencereduced leakage and improved dryness.

Exemplary chemically cross-linked cellulosic fibers suitable for adistribution layer are disclosed in U.S. Pat. No. 5,549,791, U.S. Pat.No. 5,137,537, WO9534329 or US2007/118087. Exemplary cross-linkingagents include polycarboxylic acids such as citric acid and/orpolyacrylic acids such as acrylic acid and maleic acid copolymers.

The absorbent article may also comprise an acquisition layer asadditional layer, whose function can be to quickly acquire the fluidaway from the topsheet so as to provide a good dryness for the wearer.Such an acquisition layer is typically placed directly under thetopsheet. The absorbent article may also then comprise a distributionlayer typically placed between the acquisition layer and the absorbentcore.

The acquisition layer may typically be or comprise a non-woven material,for example a SMS or SMMS material, comprising a spunbonded, amelt-blown and a further spunbonded layer or alternatively a cardedchemical-bonded nonwoven. The non-woven material may in particular belatex bonded. Exemplary upper acquisition layers are disclosed in U.S.Pat. No. 7,786,341. Carded, resin-bonded nonwovens may be used, inparticular where the fibers used are solid round or round and hollow PETstaple fibers (50/50 or 40/60 mix of 6 denier and 9 denier fibers). Anexemplary binder is a butadiene/styrene latex. Non-wovens have theadvantage that they can be manufactured outside the converting line andstored and used as a roll of material. Further useful non-wovens aredescribed in U.S. Pat. No. 6,645,569, U.S. Pat. No. 6,863,933 (both toCramer), U.S. Pat. No. 7,112,621 (Rohrbaugh), and co patent applicationsUS2003/148684 to Cramer et al. and US2005/008839 (both to Cramer).

Such an acquisition layer may be stabilized by a latex binder, forexample a styrene-butadiene latex binder (SB latex). Processes forobtaining such lattices are known, for example, from EP 149 880 (Kwok)and US 2003/0105190 (Diehl et al.). In certain embodiments, the bindermay be present in the acquisition layer in excess of about 12%, about14% or about 16% by weight. SB latex is available under the trade nameGENFLO™ 3160 (OMNOVA Solutions Inc.; Akron, Ohio).

A further acquisition layer may be used in addition to a firstacquisition layer described above. For example a tissue layer may beplaced between the first acquisition layer and the distribution layer.The tissue may have enhanced capillarity distribution propertiescompared to the acquisition layer described above. The tissue and thefirst acquisition layer may be of the same size or may be of differentsize, for example the tissue layer may extend further in the back of theabsorbent article than the first acquisition layer. An example ofhydrophilic tissue is a 13-22.5 gsm high wet strength made of cellulosefibers from supplier Havix.

If an acquisition layer is present, it may be advantageous that thisacquisition layer is larger than or least as large as an underlyingdistribution layer in the longitudinal and/or transversal dimension. Inthis way the distribution layer can be deposited on the acquisitionlayer. This simplifies handling, in particular if the acquisition layeris a nonwoven which can be unrolled from a roll of stock material. Thedistribution layer may also be deposited directly on the absorbentcore's upper side of the core wrap or another layer of the article.Also, an acquisition layer larger than the distribution layer allows todirectly glue the acquisition layer to the storage core (at the largerareas). This can give increased patch integrity and better liquidcommunication.

Fastening System 42, 44

The absorbent article may include a fastening system, for example as isknown in taped diapers. The fastening system can be used to providelateral tensions about the circumference of the absorbent article tohold the absorbent article on the wearer as is typical for tapeddiapers. This fastening system is not necessary for training pantarticle since the waist region of these articles is already bonded. Thefastening system usually comprises a fastener such as tape tabs, hookand loop fastening components, interlocking fasteners such as tabs &slots, buckles, buttons, snaps, and/or hermaphroditic fasteningcomponents, although any other known fastening means are generallyacceptable. A landing zone is normally provided on the front waistregion for the fastener to be releasably attached. Some exemplarysurface fastening systems are disclosed in U.S. Pat. No. 3,848,594, U.S.Pat. No. 4,662,875, U.S. Pat. No. 4,846,815, U.S. Pat. No. 4,894,060,U.S. Pat. No. 4,946,527, U.S. Pat. No. 5,151,092 and U.S. Pat. No.5,221,274 issued to Buell. An exemplary interlocking fastening system isdisclosed in U.S. Pat. No. 6,432,098. The fastening system may alsoprovide a means for holding the article in a disposal configuration asdisclosed in U.S. Pat. No. 4,963,140 issued to Robertson et al.

The fastening system may also include primary and secondary fasteningsystems, as disclosed in U.S. Pat. No. 4,699,622 to reduce shifting ofoverlapped portions or to improve fit as disclosed in U.S. Pat. No.5,242,436, U.S. Pat. No. 5,499,978, U.S. Pat. No. 5,507,736, and U.S.Pat. No. 5,591,152.

Barrier Leg Cuffs 34

The absorbent article may comprise a pair of barrier leg cuffs 34 and/orgasketing cuffs 32. U.S. Pat. No. 3,860,003 describes a disposablediaper which provides a contractible leg opening having a side flap andone or more elastic members to provide an elasticized leg cuff (agasketing cuff). U.S. Pat. No. 4,808,178 and U.S. Pat. No. 4,909,803issued to Aziz et al. describe disposable diapers having “stand-up”elasticized flaps (barrier leg cuffs) which improve the containment ofthe leg regions. U.S. Pat. No. 4,695,278 and U.S. Pat. No. 4,795,454issued to Lawson and to Dragoo respectively, describe disposable diapershaving dual cuffs, including gasketing cuffs and barrier leg cuffs. Allor a portion of the barrier leg and/or gasketing cuffs may be treatedwith a lotion.

The barrier leg cuffs 34 can be formed from a piece of material,typically a nonwoven, which is partially bonded to the rest of thearticle so that a portion of the material, the barrier leg cuffs, can bepartially raised away and stand up from the plane defined by thetopsheet when the article is pulled flat as shown e.g. in FIG. 5. Thebarrier leg cuffs can provide improved containment of liquids and otherbody exudates approximately at the junction of the torso and legs of thewearer. The barrier leg cuffs extend at least partially between thefront edge and the back edge of the diaper on opposite sides of thelongitudinal axis and are at least present at the longitudinal positionof the crotch point (C). The barrier leg cuffs are delimited by aproximal edge 64 joined to the rest of the article, typically thetopsheet and/or the backsheet, and a free terminal edge 66, which isintended to contact and form a seal with the wearer's skin. The barrierleg cuffs are joined at the proximal edge 64 with the chassis of thearticle by a bond 65 which may be made for example by gluing, fusionbonding or combination of known bonding means. The bond 65 at theproximal edge 64 may be continuous or intermittent. The side of the bond65 closest to the raised section of the barrier leg cuffs 34 delimitsthe proximal edge 64 of the standing up section of the leg cuffs.

The barrier leg cuffs 34 can be integral with the topsheet or thebacksheet, or more typically be formed from a separate material joinedto the rest of the article. Typically the material of the barrier legcuffs may extend through the whole length of the diapers but is “tackbonded” to the topsheet towards the front edge and back edge of thearticle so that in these sections the barrier leg cuff material remainsflush with the topsheet. Each barrier leg cuff 34 may comprise one, twoor more elastic strings 35 close to this free terminal edge 66 toprovide a better seal.

In addition to the barrier leg cuffs 34, the article may comprisegasketing cuffs 32 joined to the chassis of absorbent article, inparticular the topsheet and/or the backsheet and may be placedexternally relative to the barrier leg cuffs. The gasketing cuffs canprovide a better seal around the thighs of the wearer. Usually eachgasketing leg cuff will comprise one or more elastic string or elasticelement 33 comprised in the chassis of the diaper for example betweenthe topsheet and backsheet in the area of the leg openings.

Front and Back Ears 46, 40

The absorbent article may comprise front ears 46 and back ears 40 as isknown in the art. The ears can be integral part of the chassis, forexample formed from the topsheet and/or backsheet as side panel.Alternatively, as represented on FIG. 5, they may be separate elementsattached by gluing and/or heat embossing or pressure bonding. The backears 40 are advantageously stretchable to facilitate the attachment ofthe tabs 42 on the landing zone 44 and maintain the taped diapers inplace around the wearer's waist. The back ears 40 may also be elastic orextensible to provide a more comfortable and contouring fit by initiallyconformably fitting the absorbent article to the wearer and sustainingthis fit throughout the time of wear well past when absorbent articlehas been loaded with exudates since the elasticized ears allow the sidesof the absorbent article to expand and contract.

Elastic Waist Feature

The absorbent article may also comprise at least one elastic waistfeature (not represented) that helps to provide improved fit andcontainment. The elastic waist feature is generally intended toelastically expand and contract to dynamically fit the wearer's waist.The elastic waist feature preferably extends at least longitudinallyoutwardly from at least one waist edge of the absorbent core 28 andgenerally forms at least a portion of the end edge of the absorbentarticle. Disposable diapers can be constructed so as to have two elasticwaist features, one positioned in the front waist region and onepositioned in the back waist region. The elastic waist feature may beconstructed in a number of different configurations including thosedescribed in U.S. Pat. No. 4,515,595, U.S. Pat. No. 4,710,189, U.S. Pat.No. 5,151,092 and U.S. Pat. No. 5,221,274.

Method of Making the Article—Relations Between the Layers

The absorbent articles of the invention may be made by any conventionalmethods known in the art. In particular the articles may be hand-made orindustrially produced at high speed. Typically, adjacent layers andcomponents will be joined together using conventional bonding methodsuch as adhesive coating via slot coating or spraying on the whole orpart of the surface of the layer, or thermo-bonding, or pressure bondingor combinations thereof. This bonding is exemplarily represented for thebond between the leg cuffs 65 and the topsheet 24 on FIG. 6, and theauxiliary glues 71, 72 and microfibrous glue 51 on the detail view ofthe absorbent core on FIG. 4. Other glues or attachments are notrepresented for clarity and readability but typical bonding between thelayers of the article should be considered to be present unlessspecifically excluded. Adhesives may be typically used to improve theadhesion of the different layers, for example between the backsheet andthe core wrap. The glue may be any standard hotmelt glue as known in theart.

The absorbent core and in particular its absorbent material depositionarea 8 may advantageously be at least as large and long andadvantageously at least partially larger and/or longer than the fibrouslayer. This is because the absorbent material in the core can usuallymore effectively retain fluid and provide dryness benefits across alarger area than the fibrous layer. The absorbent article may have arectangular SAP layer and a non-rectangular (shaped) fibrous layer. Theabsorbent article may also have a rectangular (non-shaped) fibrous layerand a rectangular layer of SAP.

Experimental Settings

K(t) Method (Dynamic Effective Permeability and Uptake KineticsMeasurement Test Method)

This method determines the time dependent effective permeability (K(t))and the uptake kinetics of a gel layer formed from hydrogel-formingsuperabsorbent polymer particles or of an absorbent structure containingsuch particles under a confining pressure. The objective of this methodis to assess the ability of the gel layer formed from hydrogel-formingsuperabsorbent polymer particles or the absorbent structure containingthem to acquire and distribute body fluids when the polymer is presentat high concentrations in an absorbent article and exposed to mechanicalpressures as they typically occur during use of the absorbent article.Darcy's law and steady-state flow methods are used to calculateeffective permeability (see below). See also for example, “Absorbency,”ed. by P. K. Chatterjee, Elsevier, 1982, Pages 42-43 and “ChemicalEngineering Vol. II, Third Edition, J. M. Coulson and J. F. Richardson,Pergamon Press, 1978, Pages 122-127.

In contrast to previously published methods, the sample is notpreswollen therefore the hydrogel is not formed by preswellinghydrogel-forming superabsorbent polymer particles in synthetic urine,but the measurement is started with a dry structure. This method wasalso fully disclosed in WO2012/174026A1.

The equipment used for this method is called ‘ZeitabhängigerDurchlässigkeitsprüfstand’ or ‘Time Dependent Permeability Tester’,Equipment No. 03-080578 and is commercially available at BRAUN GmbH,Frankfurter Str. 145, 61476 Kronberg, Germany and is described below.Upon request, operating instructions, wiring diagrams and detailedtechnical drawings are also available.

Dynamic Effective Permeability and Uptake Kinetic Measurement System

FIG. 9 shows the dynamic effective permeability and uptake kineticmeasurement system, called ‘Time Dependent Permeability Tester’ herein.The equipment consists of the following main parts:

-   -   M11 Digital Laser Sensor for caliper measurement 701 (MEL        Mikroelektronik GmbH, 85386 Eching, Germany    -   Fiber for Liquid Level Detection 702 (FU95, Keyence Corp.,        Japan)    -   Digital Fiber Sensor 703 (FS-N10, Keyence Corp., Japan)    -   Precision Balance 704 (XP6002MDR, Mettler Toledo AG, 8606        Greifensee, Switzerland)    -   Power Unit Logo!Power (C98130-A7560-A1-5-7519, Siemens AG)    -   Labview Software License 706 (National Instruments, Austin, Tx,        USA)    -   Receiving Vessel 707 (5 L Glass Beaker, Roth)    -   Reservoir 708 (5 L Glass bottle, VWR) with joint 709 and        open-end tube for air admittance 723    -   Operating unit and console 705 (Conrad Electronics)    -   Computerized data acquisition system 710    -   A piston/cylinder assembly 713 as described herein    -   A controlled valve 714 (Bürkert)

FIG. 10 shows the piston/cylinder assembly 713 comprising piston guidinglid 801, piston 802 and cylinder 803. The cylinder 803 is made oftransparent polycarbonate (e.g., Lexan®) and has an inner diameter p of6.00 cm (area=28.27 cm²). The inner cylinder walls 850 are smooth; theheight of the cylinder r is about 7.50 cm. The bottom 804 of thecylinder 803 is faced with a US. Standard 400 mesh stainless-steelscreen cloth (not shown) (e.g. from Weisse and Eschrich) that isbi-axially stretched to tautness prior to attachment to the bottom 804of the cylinder 803. The piston 802 is composed of a stainless steelpiston body 805 and a stainless steel head 806. The piston head 806diameter q is slightly less than 6 cm so as to slide freely into thecylinder 803 without leaving any gap for the hydrogel-forming particleto pass trough. The piston body 805 is firmly attached perpendicularlyat the center of the piston head 806. The piston body diameter t isabout 2.2 cm. The piston body 805 is then inserted into a piston guidinglid 801. The guiding lid 801 has a POM (Polyoxymethylene) ring 809 witha diameter allowing a free sliding of the piston 802 yet keeping thepiston body 805 perfectly vertical and parallel to the cylinder walls850 once the piston 802 with the guiding lid 801 are positioned on topof the cylinder 803. The top view of the piston head 806 is shown inFIG. 11. The piston head 806 is meant to apply the pressurehomogeneously to the sample 718. It is also highly permeable to thehydrophilic liquid so as to not limit the liquid flow duringmeasurement. The piston head 806 is composed of a US. standard 400 meshstainless steel screen cloth 903 (e.g. from Weisse and Eschrich) that isbi-axially stretched to tautness and secured at the piston headstainless steel outer ring 901. The entire bottom surface of the pistonis flat. Structural integrity and resistance to bending of the meshscreen is then ensured by the stainless steel radial spokes 902. Theheight of the piston body 805 is selected such that the weight of thepiston 802 composed of the piston body 805 and the piston head 806 is596 g (±6 g), this corresponds to 0.30 psi over the area of the cylinder803.

The piston guiding lid 801 is a flat circle of stainless steel with adiameter s of about 7.5 cm held perpendicular to the piston body 805 bythe POM ring 809 in its center. There are two inlets in the guiding lid(810 and 812).

The first inlet 812, allows the Fiber for Liquid Level Detection 702 tobe positioned exactly 5 cm above the top surface of the screen (notshown) attached to the bottom (804) of the cylinder 803 once the piston802 is assembled with the cylinder 803 for the measurement.

The second inlet 810 allows connecting a liquid tube 721 providing theliquid to the experiment. To make sure that the assembly of the piston802 with the cylinder 803 is done consistently a slit 814 is made on thecylinder 803 matching a position marker 813 in the guiding lid 801. Inthis way the rotation angle of the cylinder and the guiding lid isalways the same.

Prior to every use, the stainless steel screen cloth 903 of the pistonhead 806 and cylinder 803 should be inspected for clogging, holes orover-stretching and replaced when necessary. A K(t) apparatus withdamaged screen can deliver erroneous K(t) and uptake kinetic results,and must not be used until the screen has been replaced.

A 5 cm mark 808 is scribed on the cylinder at a height k of 5.00 cm(±0.02 cm) above the top surface of the screen attached to the bottom804 of the cylinder 803. This marks the fluid level to be maintainedduring the analysis. The Fiber for Liquid Level Detection 702 ispositioned exactly at the 5 cm mark 808. Maintenance of correct andconstant fluid level (hydrostatic pressure) is critical for measurementaccuracy

A reservoir 708 connected via tubing to the piston/cylinder assembly 713holding the sample and a controller valve 714 are used to deliver saltsolution to the cylinder 803 and to maintain the level of salt solutionat a height k of 5.00 cm above the top surface of screen attached to thebottom of the cylinder 804. The valve 714, the Fiber for Liquid LevelDetection 702 and the Digital Fiber Sensor 703 are connected to thecomputerized acquisition system 710 trough the operating unit 705. Thisallows the Dynamic Effective Permeability and Uptake Kinetic MeasurementSystem to use the information from the Fiber for Liquid Level Detection702 and the Digital Fiber Sensor 703 to control the valve 714 andultimately maintain the level of the liquid at the 5 cm mark 808.

The reservoir 708 is placed above the piston/cylinder assembly 713 insuch a manner as to allow a 5 cm hydrohead to be formed within 15seconds of initiating the test, and to be maintained in the cylinderthroughout the test procedure. The piston/cylinder assembly 713 ispositioned on the support ring 717 of the cover plate 716 and the firstinlet 812 is held in place with the docking support 719. This allowsonly one position of the guiding lid 801. Furthermore, due to theposition marker 813, there is also only one position for the cylinder803. The screen attached to the bottom of the cylinder 804 must beperfectly level and horizontal. The supporting ring 717 needs to have aninternal diameter small enough, so to firmly support cylinder 803 butlarger than 6.0 cm so to lay outside of the internal diameter of thecylinder once the cylinder is positioned on the supporting ring 717.This is important so to avoid any interference of the supporting ring717 with the liquid flow.

The salt solution, applied to the sample 718 with a constant hydroheadof 5 cm can now freely flow from the piston/cylinder assembly 713 into areceiving vessel 707 positioned on the balance 704 which is accuratewithin ±0.01 g. The digital output of the balance is connected to acomputerized data acquisition system.

The caliper (thickness) of the sample is constantly measured with aDigital Laser Sensor for caliper measurement 701. The laser beam 720 ofthe digital laser sensor 701 is directed at the center of the POM coverplate 811 of the piston body. The accurate positioning of all the partsof the piston/cylinder assembly 713 allows the piston body 805 to beperfectly parallel to the laser beam 720 and as a result an accuratemeasure of the thickness is obtained.

Test Preparation

The reservoir 708 is filled with test solution. The test solution is anaqueous solution containing 9.00 grams of sodium chloride and 1.00 gramsof surfactant per liter of solution. The preparation of the testsolution is described below. The receiving vessel 707 is placed on thebalance 704 which is connected to a computerized data acquisition system710. Before the start of the measurement the balance is reset to zero.

Preparation of Test Liquid:

Chemicals needed:

-   -   Sodium Chloride (CAS#7647-14-5, eg: Merck, cat#1.06404.1000)    -   Linear C₁₂-C₁₄ alcohol ethoxylate (CAS#68439-50-9, eg. Lorodac®,        Sasol, Italy)    -   Deionized H₂O

Ten liters of a solution containing 9.00 grams per liter of NaCl and1.00 grams per liter linear C12-C14 alcohol ethoxalate in distilledwater is prepared and equilibrated at 23° C.±1° C. for 1 hour. Thesurface tension is measured on 3 individual aliquots and should be28±0.5 mN/m. If the surface tension of the solution is different from28±0.5 mN/m, the solution is discarded and a new test solution isprepared. The test solution has to be used within 36 hours from itspreparation and is considered expired afterwards.

K(t) Sample Preparation

A 10 grams representative sample of the superabsorbent polymer particlesis obtained. This is then dried in an uncovered 10 cm diameter Petridish in a vacuum chamber at 23±2° C. and 0.01 Torr or lower for 48 hoursprior to use. The sample is removed from the vacuum chamber andimmediately stored in a tightly sealed 20 mL glass airtight container at23±2° C. until further use.

2.0 g (±0.02 g) of superabsorbent polymer particles are weighed onto asuitable weighing paper using an analytical balance and transferred tothe cylinder 803 with the particles distributed evenly on the screen(not shown) attached to the bottom 804 of the cylinder 803. This is donevia sprinkling the superabsorbent polymer, while at the same timeturning the cylinder clockwise (e.g. on a circular turning table schuettpetriturn-M available at Schuett-biotec GmbH, Rudolf-Wissell-Str. 13D-37079 Göttingen Germany). An even distribution of the superabsorbentpolymer particles is critical for the measurements accuracy.

K(t) Procedure

The measurement is carried out at Tappi lab conditions: 23° C.±1° C./50%RH±2%. The empty piston/cylinder assembly 713 is mounted in the circularopening in the cover plate 716 and is supported around its lowerperimeter by the supporting ring 717. The piston/cylinder assembly 713is held in place with the docking support 719 with the cylinder 803 andpiston 802 aligned at the proper angle. The reference caliper reading(r_(r)) is measured by Digital Laser sensor. After this, the emptypiston/cylinder assembly 713 is removed from the cover plate 716 andsupporting ring 717 and the piston 802 is removed from the cylinder 803.

The sample 718 is positioned (absorbent structure) or sprinkled(superabsorbent polymer particles) on the cylinder screen as explainedabove. After this, the piston 802 assembled with the guiding lid 801 iscarefully set into the cylinder 803 by matching the position marker 813of the guiding lid 801 with the slit 814 made in the cylinder 803.

The piston/cylinder assembly is held in place with the docking support719 with the cylinder and piston aligned at the proper angle

This can be only done in one way. The liquid tube 721 connected to thereservoir 708 and the Digital Fiber Sensor 703 are inserted into thepiston/cylinder assembly 713 via the two inlets 810 and 812 in theguiding lid 801.

The computerized data acquisition system 710 is connected to the balance704 and to the digital laser sensor for caliper measurement 701. Fluidflow from the reservoir 708 to the cylinder 803 is initiated by thecomputer program by opening valve 714. The cylinder is filled until the5 cm mark 808 is reached in 5 to 15 seconds, after which the computerprogram regulates the flow rate to maintain a constant 5 cm hydrohead.The quantity of solution passing through the sample 718 is measured bythe balance 704 and the caliper increase is measured by the lasercaliper gauge. Data acquisition is started when the fluid flow isinitiated specifically when the valve 714 is opened for the first time,and continues for 21 minutes or until the reservoir runs dry so that the5 cm hyrdrohead is no longer maintained. The duration of one measurementis 21 min, laser caliper and balance readings are recorded regularlywith an interval that may vary according to the measurement scope from 2to 10 sec, and 3 replicates are measured.

After 21 min, the measurement of the 1^(st) replicate is successfullycompleted and the controlled valve 714 closes automatically. Thepiston/cylinder assembly 713 is removed and the measurements of the2^(nd) and 3^(rd) replicates are done accordingly, always following thesame procedure. At the end of the measurement of the 3^(rd) replicate,the controlled valve 714 stops the flow of liquid and stopcock 722 ofthe reservoir 708 is closed. The collected raw data is stored in theform of a simple data table, which then can be imported easily to aprogram for further analysis e.g. Excel 2003, SP3.

In the data table the following relevant information is reported foreach reading:

-   -   Time from the beginning of the experiment    -   Weight of the liquid collected by the receiving vessel 707 on        the balance 704    -   Caliper of the sample 718

The data from 30 seconds to the end of the experiment are used in theK(t) and uptake kinetics calculation. The data collected in the first 30seconds are not included in the calculation. The effective permeabilityK(t) and the uptake kinetics of the absorbent structure are thendetermined using the equation sets below.

Used Equations:

The table below describes the notation used in the equations.

A x-section of the absorbent structure sample which corresponds to thecylinder inner radius: 28.27 cm² h height of water column, 5.0 cm Δpdriving pressure applied by the 5.00 cm hydrohead (h): 4929.31 g/(cm s²)G gravity constant: 981 cm/s² η Temperature dependent effectiveviscosity of the liquid in g/(cm s) T Temperature in ° C. ρ density ofthe liquid: 1.0053 g/cm³ ρ_(s) ^(A) Apparent sample density of theporous medium or powder in g/cm³ ρ_(s) Average density of the solid partof the dry sample in g/cm³ ρ_(s k) Density of the component k of the drysample in g/cm³ M dry mass of the sample in g: 2.00 g if measuringsuperabsorbent particles m_(k) Mass of the component k of the dry samplein g V_(s) Dry sample volume in cm³ t_(i) time at step i of N discretepoints in s d_(i) caliper of the absorbent structure sample at timet_(i) in cm r_(i) reading of caliper instrument at time t_(i) in cmr_(r) reference reading of caliper instrument (reading of the piston/cylinder assembly without sample) in cm m_(out i) balance reading attime t_(i); mass of the liquid that left the sample at time t_(i) in gU(t_(i)) Sample uptake at time t_(i) in g T20 time required to reach anuptake of 20 g/g, starting at 0 s (t₀) in s U20 Sample uptake after 20minutes in g/g T80% Time required to reach an uptake of 80% of U20starting at 0 s (t₀) in s K20 Sample permeability at 20 minutes in cm²Kmin the minimum value of the permeability during the experiment in m²Kmin/K20 the ratio of Kmin and K20

The driving pressure is calculated from the hydro head as follows:Δp=h·G·ρ=4929.31 g/(cm·s²)

The caliper at each time t_(i) is calculated as the difference of thecaliper sensor reading at time t_(i) and the reference reading withoutsample:d _(i) =r _(i) −r _(r) [cm]

For superabsorbent particles samples the caliper of the sample at timet_(i)=0 (d₀) is used to evaluate the quality of the particle sprinkling.

An apparent sample density inside the cylinder can be in fact calculatedas:

$\rho_{s}^{A} = {\frac{m}{d_{0} \cdot A}\left\lbrack {g\text{/}{cm}^{3}} \right\rbrack}$

If this apparent density inside the cylinder differs from the apparentdensity of the powder by more than ±40% the measurement has to beconsidered invalid and eliminated.

The apparent density can be measured according EDANA method 406.2-02(“Superabsorbent materials—Polyacrylate superabsorbentpowders—GRAVIMETRIC DETERMINATION OF DENSITY”)

The rate of change with time of the balance reading at time t_(i) iscalculated as follows:

$\frac{d\;{m_{out}\left( t_{i} \right)}}{d\; t} = {\frac{m_{{out}_{i + 1}} - m_{{out}_{i - 1}}}{t_{i + 1} - t_{i - 1}}\left\lbrack {g\text{/}\sec} \right\rbrack}$

The rate of change with time of the caliper reading at time t_(i) iscalculated as follows:

$\frac{d\;{d\left( t_{i} \right)}}{d\; t} = {\frac{d_{i + 1} - d_{i - 1}}{t_{i + 1} - t_{i - 1}}\left\lbrack {{cm}\text{/}\sec} \right\rbrack}$

The uptake Kinetics is calculated as follows:

${U\left( t_{i} \right)} = {\frac{\left( {{A \cdot d_{i}} - V_{s}} \right) \cdot \rho}{m}\left\lbrack {g\text{/}g} \right\rbrack}$

By dry sample volume (V_(s)) is intended the skeletal volume of thesample therefore V_(s) is the actual volume occupied by the solidmaterial in the dry sample excluding pores and interstitials that mightbe present.

V_(s) can be calculated or measured by different methods known by theskilled person for example, knowing the exact composition and theskeletal density of the components it can be determined as follows:

${Vs} = {{\sum\limits_{k}^{\;}V_{k}} = {\sum\limits_{k}^{\;}{\frac{m_{k}}{\rho_{Sk}}\left\lbrack {cm}^{3} \right\rbrack}}}$

Alternatively for an unknown material composition V_(s) can be easilycalculated as follow:

$V_{S} = {\frac{m}{\rho_{S}}\left\lbrack {cm}^{3} \right\rbrack}$

The average density ρ_(s) can be determined by pycnometry with asuitable non-swelling liquid of known density. This technique cannot beperformed on the same samples subsequently used for the K(t) measuretherefore a suitable additional representative set of samples should beprepared for this experiment measurement.

From U(t) at the different time steps calculated as explained above, onecan determine the uptake at any specific time by linear interpolation.For example one of the important outputs is the uptake at 20 minutesalso called U20 (in g/g).

From U(t) at the different time steps one can also determine the timerequired to reach a certain uptake by linear interpolation. The timewhere the uptake of 20 g/g is first reached is called T20. Similarly thetime to reach any other uptakes can be calculated accordingly (e,g T5 orT10). Knowing U20 it is possible to determine from U(t) at the differenttime steps also the time to reach 80% of U20, this property is calledT80%.

The Effective Permeability is calculated as follows from the rates ofmass change and caliper change:

${K\left( t_{i} \right)} = {\eta{\frac{d_{i}}{\Delta\; p} \cdot {\left( {{\frac{1}{\rho \cdot A} \cdot \frac{d\;{m_{out}\left( t_{i} \right)}}{d\; t}} + \frac{d\;{d\left( t_{i} \right)}}{d\; t}} \right)\left\lbrack {cm}^{2} \right\rbrack}}}$

The effective viscosity of the liquid depends on the temperature and inthe interval of the experiment (23° C.±1° C.) is calculated accordingthe following empirical equation:η=−2.36·10⁻⁴ ·T+1.479·10⁻² [g/(cm s)]

From K(t_(i)) one can determine the effective permeability at a certaintime by linear interpolation. For example one of the important outputsis the permeability at 20 minutes or K20 (cm²). Similarly thePermeability at any other time can be calculated accordingly (e.g. K5 orK10).

Another parameter to be derived from the data is Kmin, which is theminimum K(t) value measured over the whole curve in the interval fromt_(i)=30 s to t_(i)=1200 s. This value is useful to calculate Kmin/K20which is the ratio between the minimum effective permeability and thepermeability at 20 minutes. This parameter express the temporary gelblocking that might occur in some of the samples. If the value is closeto 1 there is no temporary gel blocking if the value is close to 0 it isan indication that the material goes through a strong effectivepermeability drop when initially loaded with liquid.

The average values for T20, T80%, K20, U20 and Kmin/K20 are reportedfrom 3 replicates according to the accuracy required as known by theskilled man.

Centrifuge Retention Capacity (CRC)

The CRC measures the liquid absorbed by the superabsorbent polymerparticles for free swelling in excess liquid. The CRC is measuredaccording to EDANA method WSP 241.2-05.

Dry Absorbent Core Caliper Test

This test may be used to measure the caliper of the absorbent core(before use i.e. without fluid loading) in a standardized manner at thecrotch point C′ of the core or any other point.

Equipment: Mitutoyo manual caliper gauge with a resolution of 0.01 mm—orequivalent instrument.

Contact Foot: Flat circular foot with a diameter of 17.0 mm (±0.2 mm). Acircular weight may be applied to the foot (e.g., a weight with a slotto facilitate application around the instrument shaft) to achieve thetarget weight. The total weight of foot and added weight (includingshaft) is selected to provide 2.07 kPa (0.30 psi) of pressure to thesample.

The caliper gauge is mounted with the lower surface of the contact footin an horizontal plane so that the lower surface of the contact footcontacts the center of the flat horizontal upper surface of a base plateapproximately 20×25 cm. The gauge is set to read zero with the contactfoot resting on the base plate.

Ruler: Calibrated metal ruler graduated in mm.

Stopwatch: Accuracy 1 second

Sample preparation: The core is conditioned at least 24 hours asindicated above.

Measurement procedure: The core is laid flat with the bottom side, i.e.the side intended to be placed towards the backsheet in the finishedarticle facing down. The point of measurement (e.g. the crotch point Ccorresponding to this point in the finished article) is carefully drawnon the top side of the core taking care not to compress or deform thecore.

The contact foot of the caliper gauge is raised and the core is placedflat on the base plate of the caliper gauge with the top side of thecore up so that when lowered, the center of the foot is on the markedmeasuring point.

The foot is gently lowered onto the article and released (ensurecalibration to “0” prior to the start of the measurement). The calipervalue is read to the nearest 0.01 mm, 10 seconds after the foot isreleased.

The procedure is repeated for each measuring point. If there is a foldat the measuring point, the measurement is done in the closest area tothis point but without any folds. Ten articles are measured in thismanner for a given product and the average caliper is calculated andreported with an accuracy of one tenth mm.

Absorbent Article Caliper Test

The Absorbent Article Caliper Test can be performed as for the DryAbsorbent Core Caliper Test with the difference that the caliper of thefinished absorbent article is measured instead of the caliper of thecore. The point of measurement may be the intersection of thelongitudinal axis (80) and transversal axis (90) of the absorbentarticle or the crotch point C of the article. If the absorbent articleswere provided folded and/or in a package, the articles to be measuredare unfolded and/or removed from the center area of the package. If thepackage contains more than 4 articles, the outer most two articles oneach side of the package are not used in the testing. If the packagecontains more than 4 but fewer than 14 articles, then more than onepackage of articles is required to complete the testing. If the packagecontains 14 or more articles, then only one package of articles isrequired to perform the testing. If the package contains 4 or fewerarticles then all articles in the package are measured and multiplepackages are required to perform the measurement. Caliper readingsshould be taken 24±1 hours after the article is removed from thepackage, unfolded and conditioned. Physical manipulation of productshould be minimal and restricted only to necessary sample preparation.

Any elastic components of the article that prevent the article frombeing laid flat under the caliper foot are cut or removed. These mayinclude leg cuffs or waistbands. Pant-type articles are opened or cutalong the side seams as necessary. Apply sufficient tension to flattenout any folds/wrinkles Care is taken to avoid touching and/orcompressing the area of measurement.

Speed of Absorption Test

This test quantifies the speed of absorption of saline solution atdifferent times. The absorbent core to be tested is weighted to thenearest 0.1 g and the weight recorded as Dry Core Weight. The core isthen immerged flat in a container containing an excess of 0.9% salinesolution with the body-facing side of the core facing down in directcontact with liquid. The core is left in the solution for exactly 90 s.The core is then removed and the excess of saline is removed via gravityfor 20 seconds by hanging the core vertically with the back edge of thecore up. The wet core is then weighted again to the nearest 0.1 g andthe weight recorded as the 90 s Wet Weight. The core is then laid flatagain for 20 minutes on the lab bench with the body-facing side down.

At this point, the core is immerged again for 90 s in an excess of fresh0.9% saline solution again with the body-facing side facing down. Thecore is then again hanged vertical from the back of the core for 20seconds to let any excess solution drip. After this the core is weightedagain to the nearest 0.1 g and the weight recorded as 180 s Wet Weight.The following values are then calculated from the data:Speed of absorption in g/s@90 s=(90 s Wet Weight−Dry Core Weight)/90Speed of absorption in g/s@180 s=(180 s Wet Weight−Dry Core Weight)/180Mass Average Particle Size Via Sieve Test

10 g (weighed to an accuracy of at least 0.01 g) of a representativesample of the respective superabsorbent polymer particles oragglomerated superabsorbent polymer particles are sieved via sieves ofabout 10 cm in diameter (available e.g. from Retsch GmbH, Haan, Germany;DIN/ISO 3310-1). A stack of sieve with the following mesh sizes(sequence from top to bottom) is used: 850 μm, 800 μm, 710 μm, 600 μm,500 μm, 425 μm, 300 μm, 212 μm, 150 μm, pan (taken herein as equivalentto 0 μm). The weight of each empty sieve is noted down, to an accuracyof 0.01 g.

The 10 g sample is loaded to the top sieve (i.e. 850 μm) and sieved viaa sieve machine (“AS 400 control” available from Retsch GmbH, Haan,Germany) for 3 min at 250 rpm. The weight of each sieve after sieving isnoted down, to an accuracy of 0.01 g. The difference between the weightof loaded sieve and the empty sieve for each size gives the weight ofparticles per mesh size.

As size of the sieve D_(i) the sieve notation is taken, e.g. on sieve500 μm is the fraction with D500 to an amount of m500, with D500=500 μm.

The mass average particle size (mAvPS) herein is calculated as

${mAvPS} = {{\frac{\sum\limits_{i}^{\;}{m_{i} \cdot D_{i}}}{m_{total}}\mspace{14mu}{with}\mspace{14mu} m_{total}} = {\sum\limits_{i}^{\;}m_{i}}}$

EXPERIMENTALS Example of SAP Preparation: SAP1

Examples SAP1, SAP2 and SAP3 below exemplify the preparation of SAPhaving a T20 below 240 s. The process for making these superabsorbentpolymer particles can be summarize as comprising the subsequent stepsof:

-   -   providing a polyacrylic acid polymer gel; preferably wherein the        acrylic acid monomers have been polymerized at 50% to 95%        neutralization, typically using NaOH to raise the pH;    -   submitting the gel to a first grinding process and drying the        gel to obtain a base polymer;    -   rewetting, grinding, drying and sieving the resulting material,    -   optionally making a post-treatment of the resulting        superabsorbent particles such as surface cross-linking the        superabsorbent particles.

Other examples of method for making SAP having a T20 below 240 s aredisclosed in WO2012/174,026A1. The fourth, comparative, example SAP4exemplifies the making of SAP having a T20 of 341 s and did not have there-wetting step.

The first SAP example (SAP1) was made by preparing a polyacrylic acidbase polymer, followed by a rewet and grinding step and a furthersurface cross-linking step. In more details, the base polymer can beobtained according to the following procedure.

A 20000 ml resin kettle (equipped with a four-necked glass cover closedwith septa, suited for the introduction of a thermometer, syringeneedles) is charged with about 1.5 kg ice (1458.19 g) (prepared fromde-ionized water). Typically, a magnetic stirrer, capable of mixing thewhole content (when liquid), is added. An amount of glacial acrylic acid(AA) (appr. 423 g) is taken from 4000.00 g AA (for synthesis, fromMerck) to dissolve 25.68 g MethyleneBisAcrylAmide (MBAA) (for molecularbiology, for electrophoresis from Sigma Aldrich). The remaining AA isadded to the ice in 6 portions of about 250-1060 g while stirring iscontinued. A thermometer is introduced and 3330.56 g 50% NaOH solution(for analysis, from Merck) and 5944.72 g ice (prepared from de-ionizedwater) are added as follows such that the temperature is in the range of15-25° C.: The NaOH is added to the ice/AA mixture in 8 portions ofabout 215-550 g with addition of ice in 7 portions of about 420-1510 gbetween the addition of NaOH and addition of 965.52 g deionized waterafter about half of the NaOH solution is added. The MBAA solution isadded to the mixture while stirring is continued. Deionized water (therequired amount to achieve in total 12639.70 g (ice+water) minus theamount to dissolve the initiator “V50”) is added. Then, the resin kettleis closed, and a pressure relief is provided e.g. by puncturing twosyringe needles through the septa. The solution is then purgedvigorously with argon via an 80 cm injection needle while stirring atabout 400-1200 RPM. The argon stream is placed close to the stirrer forefficient and fast removal of dissolved oxygen. After about 120 min ofArgon purging and stirring 4064 mg initiator “V50”(=2,2′-azobis(N,N′-dimethyleneisobutyramidine)dihydrochloride, from WacoChemicals) dissolved in appr. 89.74 g deionized water is added to thereaction mixture while stirring and Argon purging is continued. Afterthe initiator solution is mixed with the reaction mixture (typicallyabout 3-5 min stirring and Argon purging), two photo lamps (e.g. KaiserProVision 2.55 HF equipped with 2 lamps Osram Dulux L 55W/830) areplaced on either side of the vessel. The solution typically starts tobecome turbid or a sudden increase in viscosity is observed after about5-20 min, typically at temperatures about room temperature. Then, theargon injection needle is raised above the surface of the gel andpurging with argon is continued at a reduced flow rate. The temperatureis monitored; typically it rises from about 20° C. to about 60-75° C.within 60-120 minutes. Once the temperature reaches about 60° C. orafter about 105 min after the reaction mixture becomes turbid orviscous, the lamps are switched off Once the temperature starts to drop,the resin kettle is transferred into a circulation oven (e.g. Binder FED720) and kept at about 60° C. for 15-18 hours. After this time, theresin kettle is allowed to cool at room temperature to about 20-40° C.,and the gel is removed and broken manually or cut with scissors intosmaller pieces. The gel is grinded with a grinder (e.g. meat grinderX70G from Sharpen with Unger R70 plate system equipped with pre-cutterkidney plate with straight holes at 17 mm diameter), put onto perforatedstainless steel dishes (hole diameter 4.8 mm, 50 cm×50 cm, 0.55 mmcaliper, 50% open area, from RS) and transferred into a circulation oven(Binder FED 720) at about 80° C. for about 20 hours, resulting in basepolymer 1.

The base polymer 1 thus obtained can then be wet grinded according tothe following process. 800.2 g of dried and grinded polymer resultingfrom the synthesis above were added to a 3000 ml glass beaker. A mixtureof 801.3 g of dionized water and 50 ml Ethanol (e.g. for analysis fromMerck) was quickly added to the glass beaker and the mixture was stirredquickly manually with a large lab spoon for about 5 mins. After themixing, the wetted base polymer was kept in the glass beaker for another30 mins. Following, the polymer mixture was grinded three times through3 connected mincer plates (e.g. meat grinder X70G from Sharpen withUnger R70 plate system equipped with a) pre-cutter kidney plate withstraight holes at 17 mm diameter, b) plate with 20 8 mm diameter holesand c) plate with 176 3 mm diameter holes). The feeding rate forgrinding was about 300-600 g per minute. During grinding, the wettedpolymer heats up and water and ethanol evaporates resulting in 498.2 gwetted and grinded base polymer. The wetted and grinded polymer isspread on a 50×50 cm perforated stainless steel dish (5 mm diameter) anddried in a circulation over at 120° C. for 12 hrs. The resulting driedpolymer is broken manually and ground with a cutting-grinding mill (e.g.IKA MF 10 basic grinding drive with the MF 10.1 cutting-grinding headand an outlet sieve with 1.5 mm diameter holes) and sieved to 150-710 μm(e.g. with AS 400 control from Retsch). The fraction above 710 μm isground again through the cutting-grinding mill through an outlet sievewith 1.0 mm diameter holes and again sieved through 150-710 μm. Thegrinding and sieving yields in 584.2 g grinded base polymer 1 particlesof 150-710 μm.

The grinded base polymer 1 particles can then be surface cross-linked asfollows. 500.0 g grinded superabsorbent base polymer 1 is added to aLödige Ploughshare Laboratory Mixer, Type L5 and mixed at rotary speedsetting 6. 30.05 g of Al lactate solution (15 w % Al lactate indeionized water (Aluminium L-lactate 95% from Sigma-Aldrich)) is addedvia the peristaltic pump (e.g. Ismatec MCP Standard with Tygon MHLLtube, inner diameter e.g. 1.52 mm) via a spray nozzle (spray nozzle ofMini Spray Dryer B-290 from Büchi with nozzle disc diameter 1.5 mm) at aspray pressure of about 2 bar, at a flow rate of about 3 g solution/min,at a starting temperature of about 23° C. After about 10 min theaddition of Al lactate is completed, at a temperature of about 24° C.After Al solution addition is completed, 5.01 g of Denacol EX 810solution (16 w % solution of Denacol EX 810(=EthyleneGlycolDiGlycidylEther=EGDGE) from Nagase in 1,2-propanediol(suitable for use as excipient, from Merck)) is added via theperistaltic pump and the spray nozzle at a spray pressure of about 2 barat a flow rate of about 3 g solution/min. During the addition of theDenacol EX 810 solution, the temperature stays in the range of about 23°C. After the addition is completed after about 2 min, 62.5 g ofdeionized water is added via the peristaltic pump and the spray nozzleat a spray pressure of about 2 bar at a flow rate of about 10 gsolution/min. During the addition of the deionized water, thetemperature stay at about room temperature. After about 7 min theaddition of deionized water is completed. Then, the bottom outlet of theLödige mixer is opened and the material that comes out of the bottomoutlet pushed out only by the Ploughshare mixer rotation is collectedand evenly distributed onto two Teflon coated baking trays (e.g. Kaiser7509960, 41×31×10 cm). The baking trays are covered with aluminum foiland maintained at room temperature for about 15-18 hours. After that thecovered baking trays are heated at 120° C. for 2 h 20 min in the oven(e.g. Binder APT.Line FD 240). After the heating time, the baking traysare taken out of the oven, the aluminium foil is cut, so about 3-6 slitsof about 3 cm length and about 3 mm width are created. The samples areput under a fume hood and let cool down to room temperature. Afterwards,the samples are manually broken and sieved to 150-710 μm (with sievesDIN/ISO 3310-1 e.g. from Retsch) to get the final material SAP1 in yieldof 379.4 g.

Examples of SAP Preparation: SAP2

SAP2 was made starting from the base polymer 1 used for making SAP1 asdescribed above. The further wet grinding and surface cross-linkingsteps were then conducted as follows. 1998.5 g of dried and grinded basepolymer 1 were added to a 5000 ml glass beaker and 2000 ml dionizedwater was quickly added to the glass beaker. The mixture was stirredquickly manually with a large lab spoon for about 10 mins. After themixing, the wetted base polymer was kept in the glass beaker for another30 mins. Following, the polymer mixture was grinded four times through ameat grinder (e.g. meat grinder X70G from Sharpen with Unger R70 platesystem equipped with a) plate with 20 8 mm diameter holes, b) 3 shaftedcutter knife and c) plate with 176 3 mm diameter holes). The feedingrate for grinding was about 300-600 g per minute. During grinding, thewetted polymer heats up and water evaporates. The wetted and grindedpolymer is spread on three 50×50 cm perforated stainless steel dish (5mm diameter) and dried in a circulation over at 120° C. for 12 hrs. Theresulting dried polymer is broken manually and ground with acutting-grinding mill (e.g. IKA MF 10 basic grinding drive with the MF10.1 cutting-grinding head and an outlet sieve with 1.0 mm diameterholes) and sieved to 150-710 μm (e.g. with AS 400 control from Retsch).The fraction above 710 μm is ground again through the cutting-grindingmill and sieved. The grinding and sieving yields in 1348.4 g grindedbase polymer 2 of 150-710 μm, which was cross-linked as follows.

600.3 g grinded superabsorbent base polymer 2 is added to a LödigePloughshare Laboratory Mixer, Type L5 and mixed at rotary speed setting6. 27.9 g of Al lactate solution (15 w % Al lactate in deionized water(Aluminium L-lactate 95% from Sigma-Aldrich)) is added via theperistaltic pump (e.g. Ismatec MCP Standard with Tygon MHLL tube, innerdiameter e.g. 1.52 mm) via a spray nozzle (spray nozzle of Mini SprayDryer B-290 from Büchi with nozzle disc diameter 1.5 mm) at a spraypressure of about 2 bar, at a flow rate of about 3 g solution/min, atroom temperature. After about 9 min the addition of Al lactate iscompleted. After Al solution addition is completed, 4.88 g of Denacol EX810 solution (16 w % solution of Denacol EX 810(=EthyleneGlycolDiGlycidylEther=EGDGE) from Nagase in 1,2-propanediol(suitable for use as excipient, from Merck)) is added via theperistaltic pump and the spray nozzle at a spray pressure of about 2 barat a flow rate of about 3 g solution/min. During the addition of theDenacol EX 810 solution, the temperature stays around room temperature.After the addition is completed after about 2 min, 75.2 g of deionizedwater is added via the peristaltic pump and the spray nozzle at a spraypressure of about 2 bar at a flow rate of about 10 g solution/min.During the addition of the deionized water, the temperature rises toabout 26° C. After about 7 min the addition of deionized water iscompleted. Then, the bottom outlet of the Lödige mixer is opened and thematerial that comes out of the bottom outlet pushed out by thePloughshare mixer rotation is collected and evenly distributed onto oneTeflon coated baking tray (e.g. Kaiser 7509960, 41×31×10 cm).Afterwards, the mixer is opened all other material is removed from themixer and placed onto another Teflon coated baking tray. The bakingtrays are covered with aluminum foil and maintained at room temperaturefor about 14 hours. After that the covered baking trays are heated at180° C. for 2 h in the oven (e.g. Binder APT.Line FD 240). After theheating time, the baking trays are taken out of the oven, the aluminiumfoil is cut, so about 3-6 slits of about 3 cm length and about 3 mmwidth are created. The samples in the baking trays are put under a fumehood and let cool down to room temperature. The samples are manuallybroken and sieved to 150-710 μm (with sieves DIN/ISO 3310-1 e.g. fromRetsch) to get the final material SAP2 in yield of 503.2 g.

Example of SAP Preparation: SAP3

This SAP was made as SAP2 except for the surface crosslinking of thegrinded base polymer which was made as follows. 600.4 g grindedsuperabsorbent base polymer 2 is added to a Lödige PloughshareLaboratory Mixer, Type L5 and mixed at rotary speed setting 6. 35.8 g ofAl lactate solution (15 w % Al lactate in deionized water (AluminiumL-lactate 95% from Sigma-Aldrich)) is added via the peristaltic pump(e.g. Ismatec MCP Standard with Tygon MHLL tube, inner diameter e.g.1.52 mm) via a spray nozzle (spray nozzle of Mini Spray Dryer B-290 fromBüchi with nozzle disc diameter 1.5 mm) at a flow rate of about 3 gsolution/min, at room temperature. After about 12 min the addition of Allactate is completed. After Al solution addition is completed, 4.5 g ofDenacol EX 810 solution (16 w % solution of Denacol EX 810(=EthyleneGlycolDiGlycidylEther=EGDGE) from Nagase in 1,2-propanediol(suitable for use as excipient, from Merck)) is added via theperistaltic pump and the spray nozzle at a flow rate of about 3 gsolution/min. During the addition of the Denacol EX 810 solution, thetemperature stays around room temperature. After the addition iscompleted after about 2 min, 76.2 g of deionized water is added via theperistaltic pump and the spray nozzle at a flow rate of about 10 gsolution/min. During the addition of the deionized water, thetemperature rises to about 25° C. After about 7 min the addition ofdeionized water is completed. Then, the Lödige mixer is opened all othermaterial is removed from the mixer and placed onto two Teflon coatedbaking trays (e.g. Kaiser 7509960, 41×31×10 cm). The baking trays arecovered with aluminum foil and maintained at room temperature for about14 hours. After that the covered baking trays are heated at 180° C. for2 h in the oven (e.g. Binder APT.Line FD 240). After the heating time,the baking trays are taken out of the oven, the aluminium foil is cut,so about 3-6 slits of about 3 cm length and about 3 mm width arecreated. The samples in the baking trays are put under a fume hood andlet cool down to room temperature. The samples are manually broken andsieved to 150-710 μm (with sieves DIN/ISO 3310-1 e.g. from Retsch) toget the final SAP3 in yield of 512.8 g.

Examples SAP1, SAP2 and SAP3 all had a T20 below 240 s. Comparativeexample SAP4 below describes a SAP having a T20 above 240 s.

Example of SAP Preparation: Comparative SAP4

The comparative SAP (SAP4) was made according the following steps, whichcomprised a polymerization step and a surface cross-linking step. A20000 ml resin kettle (equipped with a four-necked glass cover closedwith septa, suited for the introduction of a thermometer, syringeneedles) is charged with about 3 kg ice (2921.94 g) (prepared fromde-ionized water). Typically, a magnetic stirrer, capable of mixing thewhole content (when liquid), is added. 1178.26 g 50% NaOH solution (foranalysis, from Merck) is added to the ice and the resulting slurry isstirred. Another portion of 647.81 g ice (prepared from de-ionizedwater) is added to the stirred slurry. Subsequently, 2152.34 g 50% NaOHsolution (for analysis, from Merck) is added to the stirred slurry,typically in portions of about 600-650 g. An amount of glacial acrylicacid (AA) (appr. 481 g) is taken from 4000.02 g AA (for synthesis, fromMerck) to dissolve 25.68 g MethyleneBisAcrylAmide (MBAA) (for molecularbiology, for electrophoresis from Sigma Aldrich). The MBAA solution isadded to the mixture. A thermometer is introduced and the remaining AAand ice are added as follows such that the temperature is in the rangeof 15-25° C.: The remaining AA is added to the ice/NaOH mixture in 8portions of about 210-715 g with addition of 6145.77 g ice (preparedfrom de-ionized water) in 6 portions of about 770-1600 g between theaddition of AA while stirring is continued. Deionized water (therequired amount to achieve in total 12639.80 g (ice+water) minus theamount to dissolve the initiator “V50”) is added. Then, the resin kettleis closed, and a pressure relief is provided e.g. by puncturing twosyringe needles through the septa. The solution is then purgedvigorously with argon via an 80 cm injection needle while stirring atabout 400-1200 RPM. The argon stream is placed close to the stirrer forefficient and fast removal of dissolved oxygen. After about 60 min ofArgon purging and stirring 4014 mg initiator “V50”(=2,2′-azobis(N,N′-dimethyleneisobutyramidine)dihydrochloride, from WacoChemicals) dissolved in appr. 36.45 g deionized water is added to thereaction mixture while stirring and Argon purging is continued. Afterthe initiator solution is mixed with the reaction mixture (typicallyabout 3-5 min stirring and Argon purging), two photo lamps (e.g. KaiserProVision 2.55 HF equipped with 2 lamps Osram Dulux L 55W/830) areplaced on either side of the vessel. The solution typically starts tobecome turbid or a sudden increase in viscosity is observed after about5-20 min, typically at temperatures about room temperature. Then, theargon injection needle is raised above the surface of the gel andpurging with argon is continued at a reduced flow rate. The temperatureis monitored; typically it rises from about 20° C. to about 60-70° C.within 60-120 minutes. Once the temperature reaches about 60° C. orafter about 105 min after the reaction mixture becomes turbid orviscous, the lamps are switched off. Once the temperature starts todrop, the resin kettle is transferred into a circulation oven (e.g.Binder FED 720) and kept at about 60° C. for 15-18 hours. After thistime, the resin kettle is allowed to cool at room temperature to about20-40° C., and the gel is removed and broken manually or cut withscissors into smaller pieces. The gel is grinded with a grinder (e.g.meat grinder X70G from Sharpen with Unger R70 plate system equipped withpre-cutter kidney plate with straight holes at 17 mm diameter), put ontoperforated stainless steel dishes (hole diameter 4.8 mm, 50 cm×50 cm,0.55 mm caliper, 50% open area, from RS) and transferred into acirculation oven (Binder FED 720) at about 80° C. for about 40 hours.Once the gel has reached a constant weight (usually 2 days drying), itis ground using a centrifuge mill (e.g. Retsch ZM 200 with vibratoryfeeder DR 100, interchangeable sieve with 1.5 mm opening settings,rotary speed 8000 RPM), and sieved to 150-850 μm (e.g. with AS 400control from Retsch, with sieves DIN/ISO 3310-1 e.g. from Retsch). Theremaining fraction >850 μm is again milled and sieved to 150-850 μm.Typically, the milling step is repeated with remaining fractions >850 μmabout 1-3 times. All fractions 150-850 μm are collected and combined toform the base polymer sample. In case the residual moisture is more thanabout 6% by weight, the sample is again dried, e.g. in a circulationoven (e.g. Binder FED 720) at about 80° C. for about 5 hours. Thisdrying step might be repeated until the residual moisture is about 6% byweight or lower, e.g. about 1-5%, yielding comparative base polymer 2.

The obtained comparative base polymer 2 can then surface cross-linked toobtain comparative SAP4. 1000.11 g superabsorbent base polymer 2 asabove is added to a Lödige Ploughshare Laboratory Mixer, Type L5 andmixed at rotary speed setting 6. 60.05 g of Al lactate solution (15 w %Al lactate in deionized water (Aluminium L-lactate 95% fromSigma-Aldrich)) is added via the peristaltic pump (e.g. Ismatec MCPStandard with Tygon MHLL tube, inner diameter e.g. 1.52 mm) via a spraynozzle (spray nozzle of Mini Spray Dryer B-290 from Büchi with nozzledisc diameter 1.5 mm) at a spray pressure of about 2 bar, at a flow rateof about 3 g solution/min, at a starting temperature of about 30° C.After about 20 min the addition of Al lactate is completed, at atemperature of about 35° C. After Al solution addition is completed,9.99 g of Denacol EX 810 solution (16 w % solution of Denacol EX 810(=EthyleneGlycolDiGlycidylEther=EGDGE) from Nagase in 1,2-propanediol(suitable for use as excipient, from Merck)) is added via theperistaltic pump and the spray nozzle at a spray pressure of about 2 barat a flow rate of about 3 g solution/min. During the addition of theDenacol EX 810 solution, the temperature is in the range of about 32° C.After the addition is completed after about 4 min, 125 g of deionizedwater is added via the peristaltic pump and the spray nozzle at a spraypressure of about 2 bar at a flow rate of about 10 g solution/min.During the addition of the deionized water, the temperature is in therange of about 32° C. After about 12.5 min the addition of deionizedwater is completed. Then, the bottom outlet of the Lödige mixer isopened and the material that comes out of the bottom outlet pushed outonly by the Ploughshare mixer rotation is collected and evenlydistributed onto two Teflon coated baking trays (e.g. Kaiser 7509960,41×31×10 cm). The baking trays are covered with aluminum foil andmaintained at room temperature for about 15-18 hours. After that thecovered baking trays are heated at 120° C. for 2 h 20 min in the oven(e.g. Binder APT.Line FD 240). After the heating time, the baking traysare taken out of the oven, the aluminium foil is cut, so about 3-6 slitsof about 3 cm length and about 3 mm width are created. The samples areput under a fume hood and let cool down to room temperature. Afterwards,the samples are manually broken and sieved to 150-850 um (with sievesDIN/ISO 3310-1 e.g. from Retsch) to get the final comparative SAP4.

Base Polymer 3:

A 20 000 ml resin kettle (equipped with a four-necked glass cover closedwith septa, suited for the introduction of a thermometer, syringeneedles) is charged with about 5089.0 g of ice (ca. 30-40% of the totalamount of ice: 12128.0 g ice prepared from deionized water). A magneticstirrer, capable of mixing the whole content (when liquid), is added andstirring is started.

An 45.7 g of deionized water is taken to dissolve 4.516 g of “V50”(=2,2′-azobis(N,N′-dimethyleneisobutyramidine)dihydrochloride, from WacoChemicals) e.g. in a glass vessel with plastic snap-on cap. The vesselwith the “V50” solution is closed and set aside in a fridge at about 4°C.

312.5 g of glacial acrylic acid (AA; e.g. Acrylic Acid for synthesis,from Merck) is taken from the total amount of 4000.1 g AA to dissolve25.67 g of MBAA e.g. in a glass beaker. The beaker with the MBAAsolution is covered e.g. with parafilm and set aside.

The remaining AA is added to the ice in the resin kettle while stirringis continued.

A thermometer is introduced and in total 3330.7 g of 50% NaOH solution(for analysis, from Merck) and the remaining amount of ice (preparedfrom de-ionized water) are added subsequently in portions such that thetemperature is in the range of about 15-30° C.

The MBAA solution is added to the mixture of AA, NaOH solution and iceat a temperature of about 15-30° C. while stirring is continued. Thebeaker that contained the MBAA solution is washed 2× with deionizedwater in an amount of about 10% of the MBAA solution volume per wash.The wash water of both washing steps is added to the stirred mixture.

Deionized water (the remaining amount required to achieve the totalamount of (ice+water) of 12639.3 g minus the amount to wash the “V50”containing vessel 2× with deionized water in an amount of about 10% ofthe “V50” solution volume per wash) is added to the stirred mixture.

Then, the resin kettle is closed, and a pressure relief is provided e.g.by puncturing two syringe needles through the septa. The solution isthen purged vigorously with argon via an 80 cm injection needle at about0.4 bar while stirring at about 400-1200 RPM. The argon stream is placedclose to the stirrer for efficient and fast removal of dissolved oxygen.

After about min 1 hour and max 2 hours of Argon purging and stirring the“V50” solution is added to the reaction mixture at a temperature ofabout 20-25° C. via a syringe while stirring and Argon purging iscontinued. The vessel that contained the “V50” solution is washed 2×with deionized water in an amount of about 10% of the “V50” solutionvolume per wash. The wash water of both washing steps is added to thestirred mixture via a syringe through the septa.

After the initiator solution is mixed with the reaction mixture,stirring and Argon purging is continued for about 5 min. After that,while the reaction mixture has a temperature of about 20-25° C., twophoto lamps (Kaiser ProVision 2.55 HF equipped with 2 lamps Osram DuluxL 55W/830, at max. intensity) are placed on either side of the vesseland switched on. The solution typically starts to become turbid or asudden increase in viscosity is observed after about 5-20 min, typicallyat temperatures about room temperature. Then, the argon injection needleis raised above the surface of the gel and purging with argon iscontinued at a reduced flow rate (0.2 bar).

The temperature is monitored; typically it rises from about 23° C. toabout 60° C. within 60 minutes. Once the temperature reaches about 60°C., the lamps are switched off. Once the temperature starts to drop, theresin kettle is transferred into a circulation oven (Binder FED 720) andkept at about 60° C. for about 18 hours.

After this time, the oven is switched off and the resin kettle isallowed to cool down to about 20-40° C. while remaining in the oven.After that, the gel is removed and broken manually or cut with scissorsinto smaller pieces. The gel is grinded with a grinder (X70G fromScharfen with Unger R70 plate system: 3 pre-cutter kidney plates withstraight holes at 17 mm diameter), put onto perforated stainless steeldishes (hole diameter 4.8 mm, 50 cm×50 cm, 0.55 mm caliper, 50% openarea, from RS; max. height of gel before drying: about 3 cm) andtransferred into a circulation oven (Binder FED 720) at about 105° C.for about 18 hours.

The residual moisture of the dried gel is about 6.2% by weight.

In four baking trays (e.g. e.g. Kaiser 7509960, 41×31×10 cm) an amountof the dried gel per tray is placed and an amount of deionized water(see table below) is added at once and the solution manually stirred forabout 10 mins.

Tray 1 Tray 2 Tray 3 Tray 4 AGM amount 1500.1 g 1500.1 g 1500.2 g  714.5g Water amount 3000.0 g 3000.1 g 3005.0 g 1430.6 g

After the mixing, the wetted base polymer was kept in the trays foranother 30 mins. Following, the wetted base polymer of the four trays iscombined and grinded four times through a meat grinder (Grinder X70Gfrom Sharpen with Unger R70 plate system equipped with a) plate with 208 mm diameter holes, b) 3 shafted cutter knife and c) plate with 176 3mm diameter holes). The feeding rate for grinding was about 300-600 gper minute. During grinding, the wetted polymer heats up and waterevaporates. The wetted and grinded polymer is spread on several 50×50 cmperforated stainless steel dish (hole diameter 4.8 mm, 50 cm×50 cm, 0.55mm caliper, 50% open area, from RS) at max gel height of about 3 cm anddried in a circulation oven (Binder FED 720) at 105° C. for 18 hours andsubsequently for 2.5 hours at 105° C. and for 14 hours in an vacuum oven(e.g. Vacutherm, VT6130 P-BL, Heraeus equipped with vapour trap e.g.Titan Vapor Trap, Kinetics, and/or equipped with vacuum pump e.g.Trivac®, Leybold) at 80° C. at max. about 80 mbar.

The residual moisture of the dried gel is about 3.1% by weight.

The dried gel is then ground using a centrifuge mill (Retsch ZM 200 withvibratory feeder DR 100 (setting 50-60), interchangeable sieve with 1.5mm opening settings, rotary speed 8000 rpm). The milled polymer is againdried in an oven (e.g. Binder APT.Line FD 240) for 12 hours at 120° C.and then sieved via a sieving machine (AS 400 control from Retsch withsieves DIN/ISO 3310-1 at about 200-280 rpm for about for 5-10 min) tothe following particle size cuts with the following yields:

Code BP 3.1 BP 3.2 BP 3.3 BP 3.4 BP 3.5 BP 3.6 cut <150 μm 150-300 μm300-425 μm 425-600 μm 600-710 μm >710 μm Yield 1026.9 g 1217.0 g 876.1 g769.9 g 447.1 g 789.9 gBase Polymer 4:

A 20 000 ml resin kettle (equipped with a four-necked glass cover closedwith septa, suited for the introduction of a thermometer, syringeneedles) is charged with about 5388.3 g of ice (ca. 30-45% of the totalamount of ice: 12149.9 g ice prepared from deionized water). A magneticstirrer, capable of mixing the whole content (when liquid), is added andstirring is started.

An 43.0 g of deionized water is taken to dissolve 4.516 g of “V50”(=2,2′-azobis(N,N′-dimethyleneisobutyramidine)dihydrochloride, from WacoChemicals) e.g. in a glass vessel with plastic snap-on cap. The vesselwith the “V50” solution is closed and set aside in a fridge at about 4°C.

299.5 g of glacial acrylic acid (AA; e.g. Acrylic Acid for synthesis,from Merck) is taken from the total amount of 4000.7 g AA to dissolve25.67 g of MBAA e.g. in a glass beaker. The beaker with the MBAAsolution is covered e.g. with parafilm and set aside.

The remaining AA is added to the ice in the resin kettle while stirringis continued.

A thermometer is introduced and in total 3330.6 g of 50% NaOH solution(for analysis, from Merck) and the remaining amount of ice (preparedfrom de-ionized water) are added subsequently in portions such that thetemperature is in the range of about 15-30° C.

The MBAA solution is added to the mixture of AA, NaOH solution and iceat a temperature of about 15-30° C. while stirring is continued. Thebeaker that contained the MBAA solution is washed 2× with deionizedwater in an amount of about 10% of the MBAA solution volume per wash.The wash water of both washing steps is added to the stirred mixture.

Deionized water (the remaining amount required to achieve the totalamount of (ice+water) of 12639.3 g minus the amount to wash the “V50”containing vessel 2× with deionized water in an amount of about 10% ofthe “V50” solution volume per wash) is added to the stirred mixture.

Then, the resin kettle is closed, and a pressure relief is provided e.g.by puncturing two syringe needles through the septa. The solution isthen purged vigorously with argon via an 80 cm injection needle at about0.4 bar while stirring at about 400-1200 RPM. The argon stream is placedclose to the stirrer for efficient and fast removal of dissolved oxygen.

After about min 1 hour and max 2 hours of Argon purging and stirring the“V50” solution is added to the reaction mixture at a temperature ofabout 20-25° C. via a syringe while stirring and Argon purging iscontinued. The vessel that contained the “V50” solution is washed 2×with deionized water in an amount of about 10% of the “V50” solutionvolume per wash. The wash water of both washing steps is added to thestirred mixture via a syringe through the septa.

After the initiator solution is mixed with the reaction mixture,stirring and Argon purging is continued for about 5 min. After that,while the reaction mixture has a temperature of about 20-25° C., twophoto lamps (Kaiser ProVision 2.55 HF equipped with 2 lamps Osram DuluxL 55W/830, at max. intensity) are placed on either side of the vesseland switched on. The solution typically starts to become turbid or asudden increase in viscosity is observed after about 5-20 min, typicallyat temperatures about room temperature. Then, the argon injection needleis raised above the surface of the gel and purging with argon iscontinued at a reduced flow rate (0.2 bar).

The temperature is monitored; typically it rises from about 23-24° C. toabout 60° C. within 60 minutes. Once the temperature reaches about 60°C., the lamps are switched off. Once the temperature starts to drop, theresin kettle is transferred into a circulation oven (Binder FED 720) andkept at about 60° C. for about 18 hours.

After this time, the oven is switched off and the resin kettle isallowed to cool down to about 20-40° C. while remaining in the oven.After that, the gel is removed and broken manually or cut with scissorsinto smaller pieces. The gel is grinded with a grinder (X70G fromScharfen with Unger R70 plate system: 3 pre-cutter kidney plates withstraight holes at 17 mm diameter), put onto perforated stainless steeldishes (hole diameter 4.8 mm, 50 cm×50 cm, 0.55 mm caliper, 50% openarea, from RS; max. height of gel before drying: about 3 cm) andtransferred into a circulation oven (Binder FED 720) at about 120° C.for about 20 hours.

The residual moisture of the dried gel is about 5.8% by weight.

In four baking trays (e.g. e.g. Kaiser 7509960, 41×31×10 cm) an amountof the dried gel per tray is placed and an amount of deionized water(see table below) is added at once and the solution manually stirred forabout 10 mins.

Tray 1 Tray 2 Tray 3 Tray 4 AGM amount 1500.1 g 1500.4 g 1500.1 g  675.7g Water amount 3000.1 g 3002.1 g 3000.1 g 1353.8 g

After the mixing, the wetted base polymer was kept in the trays foranother 30 mins. Following, the wetted base polymer of the four trays iscombined and grinded four times through a meat grinder (Grinder X70Gfrom Sharpen with Unger R70 plate system equipped with a) plate with 208 mm diameter holes, b) 3 shafted cutter knife and c) plate with 176 3mm diameter holes). The feeding rate for grinding was about 300-600 gper minute. During grinding, the wetted polymer heats up and waterevaporates. The wetted and grinded polymer is spread on several 50×50 cmperforated stainless steel dish (hole diameter 4.8 mm, 50 cm×50 cm, 0.55mm caliper, 50% open area, from RS) at max gel height of about 3 cm anddried in a circulation oven (Binder FED 720) at 120° C. for 20 hours.

The residual moisture of the dried gel is about 2.7% by weight.

The dried gel is then ground using a centrifuge mill (Retsch ZM 200 withvibratory feeder DR 100 (setting 50-60), interchangeable sieve with 1.5mm opening settings, rotary speed 8000 rpm). The milled polymer is againdried in an oven (e.g. Binder APT.Line FD 240) for 12 hours at 120° C.and then sieved via a sieving machine (AS 400 control from Retsch withsieves DIN/ISO 3310-1 at about 200-280 rpm for about for 5-10 min) tothe following particle size cuts with the following yields:

Code BP 4.1 BP 4.2 BP 4.3 BP 4.4 BP 4.5 BP 4.6 cut <150 μm 150-300 μm300-425 μm 425-600 μm 600-710 μm >710 μm yield 996.4 g 1128.8 g 822.8 g829.3 g 419.2 g 750.3 g

The surface-crosslinked and agglomerated superabsorbent polymers SAP 5-9were made as follows:

600.0 g base polymer (see table) is added to a Lödige PloughshareLaboratory Mixer, Type L5 and mixed at rotary speed setting 6. Theamount of Al lactate solution (see table) (15 w % Al lactate indeionized water (Aluminium L-lactate 95% from Sigma-Aldrich)) is addedvia the peristaltic pump (e.g. Ismatec MCP Standard with Tygon MHLLtube, inner diameter e.g. 1.52 mm) via a spray nozzle (spray nozzle ofMini Spray Dryer B-290 from Büchi with nozzle disc diameter 1.5 mm) at aspray pressure of about 2 bar, at a flow rate of about 4.3 gsolution/min, at a starting temperature of about 23° C. After about 12.5min the addition of Al lactate is completed. After Al solution additionis completed, the liquid hose is disconnected, cleaned and flushed withDenacol solution (solution of Denacol EX 810(=EthyleneGlycolDiGlycidylEther=EGDGE) from Nagase in 1,2-propanediol(suitable for use as excipient, from Merck)—see table below) andconnected to the spraying unit.

The amount of Denacol EX 810 solution (see table) is added via theperistaltic pump and the spray nozzle at a spray pressure of about 2 barat a flow rate of about 4.0 g solution/min. After the addition ofDenacol EX 810 solution is completed, the liquid hose is disconnected,cleaned and flushed with deionized water and connected again to thespraying unit. After that, the amount of deionized water (see table) isadded via the peristaltic pump and the spray nozzle at a spray pressureof about 2 bar at a flow rate of about 13.6 g solution/min. After theaddition of deionized water is completed, the bottom outlet of theLödige mixer is opened and the material that comes out of the bottomoutlet pushed out only by the Ploughshare mixer rotation is collectedand evenly distributed onto Teflon coated baking trays (e.g. Kaiser7509960, 41×31×10 cm) into layers of about 2-3 cm thickness. The bakingtrays are covered with aluminum foil and maintained at room temperaturefor about 20-24 hours. After that the covered baking trays are heated at120° C. for 2 h 20 min in the oven (e.g. Binder APT.Line FD 240). Afterthe heating time, the baking trays are taken out of the oven, thealuminium foil is cut, so about 3-6 slits of about 3 cm length and about3 mm width are created. The samples are put under a fume hood and letcool down to room temperature. Afterwards, the samples are manuallybroken and sieved (with sieves DIN/ISO 3310-1 e.g. from Retsch) to getthe final materials as seen in the table below.

Final Code SAP 5 SAP 6 SAP 7 SAP 8 SAP 9 SAP 10 BP code BP 3.1 BP 4.1 BP4.2 BP 3.2 1:1 mix of 1:1 mix of BP 3.2 & BP 3.3 & 4.2 4.3 Al lactate72.06 54.03 g 54.03 g 72.02 g 54.01 g 54.03 g solution Concentration 24w % 24 w % 24 w % 24 w % 16 w % 16 w % (w %) of Denacol EX 810 solutionDenacol EX  6.05 6.01 g 6.04 g 6.00 g 6.02 g 6.04 g 810 solutionDeionized 75.09 75.06 g 75.02 g 75.02 g 72.08 g 75.09 g water Sieve cut150-850 150-850 300-850 300-850 300-850 425-850 [μm] yield 460.5 g 507.7g 519.1 g 352.3 g 423.5 g 289.2 g

The superabsorbent polymers SAP 11-12 were made by mixing twosuperabsorbent polymers as follows:

The amount of the first superabsorbent polymer (agglomerated) and theamount of the second superabsorbent polymer (see table below) wereplaced in a wide-necked 100 ml PE bottle (e.g. from VWR, Art. No.215-5631). The bottle is closed with the cap and then gently moved byhand in a rotation movement (e.g. clockwise) upside down and up again,avoiding vibrational movements (e.g. shaking) The rotational movement iscontinued for about 1 min, performing about 40-60 rotations.

Final Code SAP 11 SAP 12 First SAP SAP 5 SAP 6 Amount of first SAP  8.0g  8.0 g Second SAP SAP 2 SAP 2 Amount of Second SAP 12.0 g 12.0 gProperties of the SAPs Exemplified:

The properties of the SAP were measured and the results are as follows.T20 and U20 were measured with 3 replicates, except otherwise indicated(n=).

SAP 1-3 and SAP 7-12 are examples having a T20 below 240 s.

SAP 4 is a Comparative example.

SAP 7-12 contain agglomerated superabsorbent polymer particles.

T20 CRC FSR UPM U20 (s) (g/g) (g/g/s) (10⁻⁷ cm³ · s/g) (g/g) SAP1 (usedin Core 194 25.4 0.27 64 28.3 Example 1) SAP2 211 26.1 0.19 99 29.7 SAP3188 27.7 0.24 41 31   SAP4 (used in 341 26.7 0.15 55 27.3 ComparativeCore Examples 1 and 2) SAP 7 117 24.3 0.55 71 27.9 SAP 8 108 23.2 0.5590 25.9 (n = 4) (n = 4) SAP 9 104 25.2 0.59 49 29.3 SAP 10 199 29.1 0.2958 30.9 SAP 11 192 23.1 0.62 53 27.0 (n = 1) (n = 1) SAP 12 164 24.00.61 47 28.0 (n = 2) (n = 2)

SAP1 and comparative SAP4 were used in the core examples described inmore details below.

Absorbent Core Examples

Invention example 1, described in details below, is an absorbent corewhich illustrates the present invention. The core of example 1 comprisedtwo channels similar to those shown in FIG. 1 and the SAP describedabove having a T20 of 194 s. Comparative example 1 comprised the SAPhaving a T20 of 341 s and no channels. Comparative example 2 comprisedthe same channels as example 1 and the same SAP as comparative coreexample 1 (SAP4).

The core of example 1 was made by combining two absorbent layers. Thefirst absorbent layer comprised as first substrate a 420 mm long and 165mm wide hydrophilic nonwoven web (SMS, i.e. spunbond-meltblown-spunbondlayers) made of polypropylene and having a basis weight of 10 g/m². Thissubstrate was positioned on a vacuum table 800 as shown schematically onFIG. 8. The table comprises a rigid support comprising a series oftransversal support ridges 840 and two channel shaped ridges 820. Thevacuum holes 830 are formed between these ridges. The vacuum areas wereeach 8 mm wide (MD) and 110 mm long (CD), except in the area where thechannel shaped ridges were present, the width of the transversal ridgeswas 2 mm (MD) for a total of 36 parallel stripes.

The nonwoven substrate was positioned on the vacuum table. A net ofMicrofiber glue (NW1151ZP ex. FULLER ADHESIVES) was evenly applied onthe substrate at an average basis weight of about 10 g/m² and a width of110 mm, covering the whole length of the substrate. The vacuum patternwas divided in 6 zones starting from the 1^(st) stripe. Area 1 was 40 mmlong in MD. Zones 2 to 5 are 60 mm wide and zone 6 was 80 mm wide. Withvacuum helping immobilizing the SAP in the desired regions, the SAP washomogeneously distributed within each zone according to the below table.The pre-determined amount of SAP was distributed for each zone with theaid of shaped silicon paper matching exactly the vacuum table design.

Zone 1 2 3 4 5 6 Total Length (mm) 40 60 60 60 60 80 360 SAP amount (g)0.81 1.37 1.71 1.58 0.97 0.61 7.05

As a result, the SAP was applied in stripes matching the pattern of thevacuum table. The overall amount of superabsorbent polymer material inthe first absorbent layer was 7.05 g. Subsequent to the application ofthe SAP, a net of Microfiber glue (first adhesive) was evenly applied,at an average basis weight of about 10 g/m² and a width of 110 mm,covering the whole length of the first absorbent layer. The two curvedSAP free materials area were further fitted with a double side adhesive(1524-3M transfer adhesive with a width 6.4 mm) along the channel areaon the nonwoven. This was to ensure sufficient bond strength of thechannels during the further testing of these hand-made absorbent cores.In an industrial process, the pressure and the adhesive used asauxiliary glue is normally sufficient to ensure a strong bond withoutthe need of a double sided tape.

The second absorbent layer comprised as second substrate a 420 mm longand 130 mm wide SMS nonwoven web made of polypropylene and having abasis weight of 10 g/m². The second absorbent layer was formed using asimilar vacuum table and absorbent material and glue as the firstabsorbent layer, with the transversal ridges shifted by a few mm so thatthe land and junction areas of the opposed absorbent layer match eachother.

The first and the second absorbent layers were combined by placing themtogether such that the sides of both carrier substrates, which were notcovered by superabsorbent polymer material were facing outwardly.Thereby the laminate absorbent core is formed with the superabsorbentpolymer material enclosed between the first and second carriersubstrate. The first and second absorbent layers were combined such thateach SAP stripe was placed to match the gap between the stripes of theabsorbent layer directly opposed. Hence, each SAP stripe of the upperlayer is placed centrally in the respective gap between twosuperabsorbent polymer material stripes of the lower laminate layer andvice versa in order to provide a substantially continuous combinedabsorbent layer.

After the two absorbent layers are combined, the external edges of thefirst substrate were folded over the second substrate so that thecombined core structure had a width of 120 mm. In these hand-madesamples, the flaps on each side were fixed with a stripe of double sideadhesive (1524-3M transfer adhesive with a width 6.4 mm) of 420 mm, butin an industrial process a standard hotmelt glue can be used to seal thelongitudinal sides of the core.

Comparative Example 1

Comparative example 1 was made as example 1 with the differences thatthe vacuum table did not comprise channel forming ridges and that theSAP4 having a T20 of 341 s was used. Thus this absorbent core did notform channels when absorbing a liquid. The same amount of SAP and theirrepartition in the zones was used.

Comparative Example 2

Comparative example 2 was made as example 1 using the same vacuum tableto form the same areas free of SAP as Invention Example 1. The SAP usedfor this absorbent core was the same SAP4 as in Comparative Example 1having a T20 of 341 s.

Test Results

The Speed of Absorption Test described above was conducted on fivesamples. The results were averaged and are reported in the Table below.

Speed g/s @90 s Speed g/s 180@s Comparative Example 1 1.74 1.55 (withoutchannels) Comparative Example 2 1.73 1.50 (with channels) InventionExample 1 2.26 1.79

Comparative examples 1 and 2 show that for the first 90 s of the test,the presence or absence of the channels did not significantly influencethe speed of absorption. At 180 s however, the speed of acquisition ofthe core with the channels was significantly worse (minus 0.05 g/s) thanthe same core without the channels (at 95% confidence with t-Studenttest). The core of the invention example 1 showed an acquisition speedat 180 s of 1.79 g/s, which was significantly higher than the speed ofthe conventional AGM at 180 s or even at 90 s.

Misc

The dimensions and values disclosed herein are not to be understood asbeing strictly limited to the exact numerical values recited. Instead,unless otherwise specified, each such dimension is intended to mean boththe recited value and a functionally equivalent range surrounding thatvalue. For example, a dimension disclosed as “40 mm” is intended to mean“about 40 mm.”

Every document cited herein, including any cross referenced or relatedpatent or application, is hereby incorporated herein by reference in itsentirety unless expressly excluded or otherwise limited. The citation ofany document is not an admission that it is prior art with respect toany invention disclosed or claimed herein or that it alone, or in anycombination with any other reference or references, teaches, suggests ordiscloses any such invention. Further, to the extent that any meaning ordefinition of a term in this document conflicts with any meaning ordefinition of the same term in a document incorporated by reference, themeaning or definition assigned to that term in this document shallgovern.

While particular embodiments of the present invention have beenillustrated and described, it would be obvious to those skilled in theart that various other changes and modifications can be made withoutdeparting from the spirit and scope of the invention. It is thereforeintended to cover in the appended claims all such changes andmodifications that are within the scope of this invention.

What is claimed is:
 1. An absorbent article for personal hygiene comprising: a liquid permeable topsheet; a liquid impermeable backsheet; an absorbent core disposed between the topsheet and the backsheet; and an acquisition/distribution layer disposed between the absorbent core and the topsheet; wherein the absorbent core comprises: a core wrap enclosing an absorbent material comprising a combination of superabsorbent polymer particles and airfelt, the core wrap comprising a top side and a bottom side; one or more areas substantially free of absorbent material through which the top side of the core wrap is attached to the bottom side of the core wrap, so that when the absorbent material swells the core wrap forms one or more channels along the areas substantially free of absorbent material; wherein the superabsorbent polymer particles have a time to reach an uptake of 20 g/g (T20) of less than 240 s, as measured according to the K(t) test method; and wherein ditches are formed via deformation of the acquisition/distribution layer into the one or more channels.
 2. The absorbent article of claim 1 wherein the superabsorbent polymer particles have a time to reach an uptake of 20 g/g (T20) of from about 40 s to less than about 240 s.
 3. The absorbent article of claim 1 wherein the superabsorbent polymer particles comprise agglomerated superabsorbent polymer particles.
 4. The absorbent article of claim 1 wherein the absorbent material comprises at least about 70%, of superabsorbent polymer particles by weight of the absorbent material, and wherein the absorbent core comprises from about 2 g to about 50 g of superabsorbent polymer particles.
 5. The absorbent article of claim 1 wherein the absorbent core comprises from about 5 g to about 40 g of superabsorbent polymer particles.
 6. The absorbent article of claim 1 wherein the absorbent core comprises at least a pair of areas substantially free of absorbent material.
 7. The absorbent article of claim 1 comprising an auxiliary glue between the absorbent material and the top side and/or the bottom side of the core wrap.
 8. The absorbent article of claim 1 wherein the absorbent core has a caliper measured at the core's crotch point (C′) of from about 0.2 to about 4 mm.
 9. The absorbent article of claim 1 wherein the superabsorbent polymer particles have an UPM value of from about 40.10⁻⁷ cm³·s/g to about 500.10⁻⁷ cm³·s/g and/or the superabsorbent polymer particles have a CRC value of from about 18 g/g to about 40 g/g. 